While research is abundant on quality assurance in higher education, very little has been done to study informal learning in general and its relation to quality assurance in particular. Reporting on a study of informal learning among PhD students in natural sciences in an Iranian university, this article is an attempt to address this issue. Qualitative data from interviews and quantitative data from a questionnaire were used to investigate the extent to which a group of science PhD students resorted to informal learning strategies. The results suggest that far from a team-working culture one might expect to find among PhD students in the natural sciences, they often conceived of themselves as solitary researchers within the confines of their laboratories. It is argued that this is at least partly due to the reduction of the managerial role of PhD supervisors in the context under study. Given the significant role of informal learning among university students in general, and PhD students in particular, this should be incorporated into quality assurance procedures. (Contains 4 tables.)