Over the past thirty years there has been a significant turn towards practice and away from institutions in sociological frameworks for understanding science. This new emphasis on studying ‘science in action’ ( LATOUR 1987 ) and ‘epistemic cultures’ ( KNORR CETINA 1999 ) has not been shared by academic and policy literatures on the problem of women and science, which have focused on the marginalisation and under-representation of women in science careers and academic institutions. In this paper we draw on elements of both these approaches to think about epistemic communities as simultaneously practical and organisational. We argue that an understanding of organisational structures is missing in science studies, and that studies of the under-representation of women lack attention to the detail of how scientific work is done in practice. Both are necessary to understand the gendering of science work. Our arguments are based on findings of a qualitative study of bioscience researchers in a British university. Conducted as part of a European project on knowledge production, institutions and gender the UK study involved interviews, focus groups and participant observation in two laboratories. Drawing on extracts from our data we look first at laboratories as relatively unhierarchical communities of practice. We go on to show the ways in which institutional forces, particularly contractual insecurity and the linear career, work to reproduce patterns of gendered inequality. Finally, we analyse how these patterns shape the gendered value and performance of ‘housekeeping work’ in the laboratory.