This paper analyses a large database on inter-firm R&D cooperation formed in the pharmaceutical biotechnology industry during the period 1985 - 1998. The results indicate that network size largely grows, whereas the density of the network declines during the periods. In the network analysis that emphasizes individual structural positions, the empirical results show that small biotechnological companies had a crucial bridging role for the large pharmaceutical firms in the second half of the 1980s. In the 1990s, the bridge role of biotechnology companies became less important and established pharmaceutical companies developed into dominant start players with many collaborators while holding central roles in the research network. The current analysis also shows that degree-based and betweenness-based network centralization are both low implying that the overall positional advantages are relatively equally distributed in the inter-firm R&D network of the pharmaceutical biotechnology industry.