There has been no attempt to explain the variation in stock market responses to alliance announcements in an era of industry ferment, to reflect the benefits and costs associated with the evolving structural topologies of firms¿ alliance networks. This study investigates such effects using data from firms in the UK biotechnology industry in 1986-2000, an era of industry ferment, at the ego-network and the ¿whole¿-network level. The findings highlight the value of managing a firm¿s alliance ego-network as a strategic tool that provides network resources but also affects others¿ perceptions of a firm¿s resources and growth prospects.