We investigate share price responses to the formation of 237 partnerships in the biotechnology/pharmaceutical industry spanning 1995-2000. The average stock price response is positive, more so than in previous empirical works, which could be interpreted as evidence that interfirm collaboration is particularly valuable in high-technology industries. We find no evidence of wealth transfers. While all sorts of alliances can be associated to significantly positive returns, more value accrues to the partnership when it involves the creation or the transfer of technological knowledge. Looking at the firm characteristics, we conclude that being the smaller partner in a technological alliance generates higher abnormal returns (while no correlation is found in non-technological partnerships). Finally, the stock market value associated to the partnership increases with the profitability of the member firm.