Shares in healthcare firm Amersham have soared after the company said it had been approached about a possible takeover bid.
In a short statement, the firm said it had received "an approach which may or may not lead to an offer for the company as a whole".
At one point shares in the diagnostics and drug research equipment firm were up by a quarter, but by the close they had fallen back to stand 89.5p, or 14%, higher at 641p.
Amersham employs more than 10,000 people worldwide and recorded sales of £1.62bn ($2.54bn) last year.
Opinion was divided among analysts as to who might have made the approach.
"We think it is someone already involved in the diagnostic business," said WestLB analyst Paul Diggle.
"Someone like Roche or Abbot Labs, someone significantly bigger than Amersham," he said.
But ING Financial Markets analyst Max Herrmann said the approach was more likely to have come from a company trying to break into the diagnostic business.
"The obvious names are people in this area like Tyco, Schering, Braco and BMS, formerly DuPont -- but I think there would be too many issues with any of them," Mr Herrmann said.
Merger activity has been picking up in the healthcare sector as companies have sought to broaden their influence.
"If you compare healthcare with any other global industry, like automotive or consumer electronics, it is clear it is still heavily fragmented," said Martyn Postle, head of consultants Cambridge Healthcare & Biotech.
"Companies are realising that in order to maintain historic growth rates you need a global market access capability."
Amersham, based in Buckinghamshire, was created in 1997 from the merger of the UK's Amersham International, Sweden's Pharmacia Biotech and Norway's Nycomed.
It is organised into two businesses - Amersham Health and Amersham Biosciences.
Amersham Health develops imaging agents which enhance medical scans to help the early detection of disease.
Amersham Biosciences provides technology to help the research and manufacture of drugs.