The shares slumped another 102p to 2,508p. Since peaking at 2,315 last month they have been in almost relentless retreat. To some extent Bio is a victim, of its own success.
Last month it produced what can only be described as encouraging data about its Marimastat cancer drug. There are high hopes the phase III trials are going well and the treatment will have a realistic chance of being launched and becoming a legendary drugs blockbuster.
But, paradoxically, Marimastat's progress has raised stock market doubts about Bio's valuation.
Merrill Lynch set the cat among the pigeons when it said the shares were 30 per cent too high.
And with many investors sitting on huge profits - the shares have climbed from 462p since July - the temptation to lock in at least some of their rewards have proved irresistible.
This week there has been some heavy selling with one stockbroker unloading 1.2 million shares. Although that particular block was quickly mopped up sellers have kept the upper hand with the result that the fall has, in effect, become self-feeding, prompting more and more investors to take at least some of their profits.
Bio has experienced similar slides before. Each time, after shaking out nervous holders, the shares have rallied strongly. But this time round the jitters seem far more pronounced.
But as one drugs company looks in need of an injection another is riding high. Scotia Holdings was yesterday's star, jumping 55p to 778p as stories buzzed that a positive analytical note was about to appear. One suggestion was Scotia had met one leading investment house, thought to be Kleinwort Benson. The shares were 423p a year ago. Chiroscience was also in form, up 22p to 469p.
Oxford Molecular fell 8p to 329p as Cazenove placed 7.5 million shares at 320p. Original venture capitalist backers was thought to be selling. Last month Caz placed 15 million shares in the drugs software group, at around 300p.
The rest of the market dozed fitfully in a mid-summer haze. Once again it ignored a firm New York. After struggling throughout the session to hang on to a modest gain it surrendered in the last hour, ending 5.2 points down at 3,722.3. The futures expiry went smoothly.
GRE edged forward 2p to 260p as bid stories resurfaced. Commercial Union, the favourite to pounce, shaded 4p to 574p.
Another financial share, Schroders, had a lively session as Barclays de Zoete Wedd made positive noises. Ordinary shares jumped 32p to 1,360p and the non voters 20p to 1,048p.
Whitbread, still suffering from the reported row with David Lloyd, had to contend with rumours it was about to pay pounds 50 to pounds 60m for the Oddbins off-licence chain. The shares, with ABN Amro Hoare Govett saying they are overvalued, fell 11.5p to 718.5p.
Pelican, the restaurant chain which should serve up appertising year's figures next week, added 4p to 157p. It is regarded as a possible Whitbread target.
Jarvis Hotels when issued shares ended at 180p after being priced at 175p. They touched 193p with Seaq turnover put at 20.4 million shares.
Utilities continued to enjoy takeover speculation with at least two US groups, Florida Power and Houston Industries, said to be on the prowl. Southern Electric, seen as an anxious predator after its Southern Water failure, gained 13p to 715p.
Yorkshire Tyne Tees Television hardened to 1,138p as NatWest Securities lifted its profit forecasts. It expects pounds 17.5m this year, rising to pounds 81m in 1999.
Mersey Docks & Harbour slumped 26p to 378p following the escalation of its dockers dispute. BBA held at 313p. It is taking analysts to see its Swedish operations next week, a jaunt which is regarded as a bridge building exercise following its short lived intervention in the Lucas Industries/Varity merger.
The brighter outlook for the housing market lifted estate agents, Hambro Countrywide 8p to 86p and John D Wood 5p to 60p. Hambros, the merchant bank controlling Countrywide, added 4p to 230p.
Rhino, the video games retailer to be called Electronics Boutique, gained 1.5p to 17.5p following an encouraging statement. Chairman Joe Firestone said a 60 per cent sales increase had been achieved in 19 remodelled outlets.
Tullow Oil rose 3p to 86p as stories filtered through that a rights issue may be rolled out next week.
There were suggestions of a one-for-eight call at 80p. The company has interests in Britain, Senegal, India and the Czech Republic but it is its involvement in Pakistan which is the jewel in its crown. Development of the Pakistani fields could prompt the cash call.
There is also speculation that Tullow has had bid approaches - British Gas is one name in the frame.
Vision, a leader in miniature camera technology, will suffer further losses in the year ending next month but then move into profit, stockbrokers Albert E Sharp and Greig Middleton agree. Sharp looks for pounds 3m and GM pounds 3.7m. The shares held at 288p.