This paper presents an analysis of networks among small and medium-sized enterprises in the Irish biotech sector. The study applies social network analysis to determine the structure of networks of company directors and inventors in the biotech sector. In addition, on the basis of interviews, this article analyses the extent of actual knowledge flow through these industry networks. The paper makes both a theoretical and methodological contribution to innovation network research. In relation to theory, the findings of the social network analysis indicate that the extent and path of knowledge flow are influenced by both the type of knowledge in question and whether the network is of a formal or informal nature. Methodologically, the results of this paper raise questions about the application of social network analysis in innovation studies.