Scientists at London's Birkbeck College and Moscow's Institute of Genetics of Micro- Organisms have discovered that the festive plant contains a chemical similar to Ricin, which is already used in chemotherapy.
The researchers are now working with a German company, Medaus of Cologne, to turn the office party aphrodisiac into an anti-cancer drug. It has a particularly large molecule that would help it stick effectively to malignant cells while the poison kills them off. The scientists hope to tether it to antibodies that would seek out and attack cancerous cells.
"It is particularly promising," says Dr Rex Palmer, reader in Crystallography at Birkbeck College, who has been working out how the chemical works.
"We may now be able to employ genetic engineering to make it work more effectively in treating cancer and leukaemia and countering rejection after transplant surgery."
But today's scientists may be some 2,000 years behind the Druids. The Roman historian Pliny, writing in the first century AD, noted how the Druids "call the mistletoe by a name meaning, in their language, the all- healing". He listed 11 conditions which mistletoe could treat, ranging from malformed males to epilepsy. Most intriguingly, he noted that it could be used to "disperse tumours".
Lindow Man, a 2,300-year-old human sacrifice found in a peat bog in Cheshire in 1984, had three grains of mistletoe pollen still in his stomach. It is thought that he may have been treating himself for cancer.
Pliny recorded that the Druids "hold nothing more sacred" than the mistletoe and described how priests clad in white would climb trees to cut it down with golden sickles. The cut twigs would be caught in white cloths so that they would not lose their healing powers by touching the ground.
"The Druids appear to have been right," says Dr Palmer. "They must have been on to something. After all, they built Stonehenge."