Soaring to a new all-time high of 919p in the morning, up 114p from Thursday's close, they then hurtled back down to 507.5p on news that US trials of a new test for heart attacks had hit the buffers.
But the bulls who are behind the shares' amazing rise from 130p since the end of January recovered their nerve and late buying left the shares down just 137.5p on the day at 667.5p.
With around 7 per cent of the company's share capital traded yesterday, the Stock Exchange was understood to be investigating the "unusual" movements in the price. David Evans, Shield's finance director, said the Exchange had "made due inquiry" after several one-day price changes of more than 10 per cent since the beginning of February.
The crash in the shares came after Shield announced that key trials in Houston, Texas, based on 700 patients who had been involved in a long- running government programme, had been nullified by the mishandling of some samples dating back to 1986.
The trial, alongside another in London's St Bartholomew's Hospital, is testing whether Shield's Activated Factor Twelve accurately predicts heart attacks.
The recent soaring share price has been fuelled by a positive report on the trials issued by the company earlier this year. But Mr Evans said precipitate - "gunge" - had been discovered in the samples, making them statistically invalid as a basis for the trial.
The company said it would be going back to those in charge of the trial to see if later data could be substituted, but he said Shield would go ahead with a briefing to investors on 24 March.
Analysts have suggested the market for the product could match the 500 million cholesterol test kits sold world-wide every year, but others are highly sceptical. One said: "I think it's a classic stock market ramp. A small biotech company with great development plans and you ramp it to hell and back."Reuse content