The news that Biogen Idec’s chief executive James Mullen is to retire has led observers to start mulling over what the future of the US biotechnology will look like.

Mr Mullen, 51, is leaving on June 8 having headed up the firm for 21 years and Biogen says it has initiated a search for his successor. The announcement comes seven months after dissident shareholder Carl Icahn managed to get two representatives onto the company’s board.

Mr Icahn has been at loggerheads with Biogen for a couple of years and criticised the company’s management for not looking hard enough to find a buyer and its decision to take down the ‘for sale’ sign in December 2007. Other investors who seemed less than happy with Mr Mullen’s reign included HealthCor Management, a New York-based hedge fund, which in November criticised the CEO’s pay and incentives package as “inconsistent with Biogen Idec’s poor stock performance”.

Healthcor issued a statement saying “we anticipate that Mr Mullen's successor will be more focused on improving Biogen's R&D productivity and efficiency”. The company recently failed to entice partner Facet Biotech worth a $420 million offer to merge and it remains to be seen whether the new person in charge will look for acquisitions or indeed get the ‘for sale’ signs out of the cellar.

Last May, Mr Icahn suggested that Biogen should be split in two, with one firm focusing on neurology and the other on cancer and autoimmune diseases.