If you suffer from hay fever and find your condition soothed after visiting a Chinese restaurant, shitake mushrooms may well be the reason. Scientists have discovered that the shitake (Lentinula edodes), which is commonly used in Chinese and Japanese cooking, has antihistamine properties.

Another compound isolated from the shitake has been shown to be useful in the treatment of stomach cancers. Shitakes are not alone in the field of fungi that possess important medicinal properties.

As many as 220 anti-tumour and 42 anti-viral agents have been isolated from fungi. Some fungi have antibiotic properties, others lower blood pressure or quieten spasms.

Drugs derived from mushrooms are in use in transplant surgery (cyclosporin-A), childbirth (derivatives of ergot) and the treatment of malnourished children. In the past alcoholics have been given coprine, a toxic agent present in the common ink-cap mushroom (Coprinus atramentarius), and psychotics have been treated with psilocybin, found in some hallucinogenic mushroooms.

Fungi, some claim, even helped to win the war. Penicillin, as most people know, comes from the fungus Penicillium, a familiar blue or green mould which grows on rotten food. The development in the early Forties of a means of mass producing the culture obtained from mouldy cantaloupe melons enabled enough penicillin to be obtained to supply all Allied troops from D-Day onwards.

Our early ancestors nurtured crude cultures of medicinal moulds as a kind of living, antibiotic 'sticking plaster'. These moulds may well have contained penicillin or one of the other fungal antibiotics in use today, such as cephalosporin or fusidic acid. Certainly they must have had some beneficial effect as 'mould therapy' was popular until modern antibiotics took over.

Patents have been taken out on fungal mycelium dressings for wounds. Although not antibiotic, the fibrous mass of branching filaments that makes up a fungus's body, extracted from Mucor mucedo and Rhizomucor meihei, retains moisture and promotes rapid healing when applied to wounds.

The appearance in the mid-Seventies of cyclosporin-A, the fungal immune system supressor, was almost as significant as that of penicillin. Recovered from the fermentation broth of the fungi Trichoderma polysporum and Cylindrocarpon lucidum, cyclosporin-A heralded a dramatically increased success rate in the transplant of bone marrow, liver and pancreas, and with fewer side-effects.

Children in the Third World have also benefited from fungi. An intolerance to milk caused by a deficiency involving the enzyme lactase means that some are unable to metabolise milk. Instead of being absorbed, the milk's goodness is fermented to gas. This deficiency can be overcome by adding to the milk fungal lactase, Aspergillus oryzae and Candida lipolytica. Other fungal enzymes have been found to be useful in the treatment of alimentary dyspepsia, blood clots, gout and even tooth decay.

Practitioners of Chinese medicine continue to use fungi, as they have for centuries, recognising anti-cancer and anti-viral properties. The caterpillar fungus came to the attention of the Western world last year when it was revealed to be the 'secret potion' which enabled Chinese women athletes to run like the wind. The drug contained in the caterpillar, or cordyceps, fungus is the antibiotic cordycepin, produced by the fungus for its own use. It makes sure that the larva on which it is feeding does not disintegrate at death so that the fungus can feed on internal organs.

In traditional Chinese medicine cordyceps is prescribed for a host of ailments, including tuberculosis, anaemia, and mental and physical weariness. It is perhaps this last use which assists the athletes in their training regimes. Tests on cordyceps support at least some of the claims.

American research in the Thirties showed that penny-bun (Boletus edulis) and giant puffball (Calvatia gigantea), two fungi common to this country, inhibit certain types of cancer. Unfortunately, further research has been hampered by the unwillingness of either fungus to grow under controlled conditions. Also it takes 1,500lbs of puffball to produce just a pound of the active principle calvacin.

English folk medicine has also made use of fungi. Cramp ball (Daldinia concentrica) is a round, blackish fungus that grows mainly on the bark of ash trees. In earlier times it was carried in the pocket to ward off cramp. Common stinkhorn (Phallus impudicus), the famously phallic-shaped fungus, was eaten in its immature 'egg' stage as an aphrodisiac and to cure impotence. There is, however, no scientific evidence for these beliefs.

But the potency of ergot of rye (Claviceps purpurea) is established. During the Middle Ages bread made from contaminated rye caused widespread epidemics of gangrene, cramps, convulsions and hallucinations known as Holy Fire or St Anthony's Fire.

One of its many effects is to contract the uterus. Small doses of ergot were used to hasten childbirth from the 16th century. In modern medicine one of the active principles in ergot, ergometrine, is administered after childbirth to prevent haemorrhaging and to help return the uterus to its normal size.

It can also cause hallucinations, as can fly agaric (Amanita muscaria), liberty cap (Psilocybe semilanceata), and some of the Psilocybe and Inocybe mushrooms. Medicine men and women in different cultures have used hallucinogenic mushrooms to induce trance-like states of awareness.

People who like a drink should know that while the common ink- cap can be eaten in perfect safety, if they drink alcohol in the next few days they risk being overcome with nausea, sweating, acute sensations of pins and needles and heart palpitations. In the past the active substance coprine has been used to deter alcoholics from drinking. Modern medicine has something similar in the drug disulfiram.

To date, only a handful of the thousands of fungal species known to man have been tested for medicinal use. Who knows what further cures lie within their complex biochemical structures. The day may not be far off when there are more mushrooms in the medicine cabinet than in the frying pan.