Women face consistent disadvantages in their experiences in organizations, as evidenced by inequities in interpersonal attractiveness, social isolation, job satisfaction, and work strain. The question raised is whether these disadvantages are due simply to differences in access to key organizational resources (expertise, professional rank, and authority), or to the advantages men have in real izing their vested interests in the face of competition from women. The vested interest interpretation receives strong inferential support, while the interpretation based on differential access to resources receives little confirmation. The concept of compartmentalized rationality is developed in.exploring the implications of the findings. Differences in the experiences of women and men in some sorts of social activity have been much studied and, as a result, are generally familiar in the discipline. Yet, in organizational research, direct comparisons between men and women are rare. The reasons for this vary. Some have speculated that women react to work in organizations in a fundamentally different way than men do (Etzioni), and this has occasionally caused women to be excluded from an analysis altogether (Shepard). Others have studied women at work but have not explored the importance of sex, per se, in determining behavior. (For a comment on this, see Acker and van Houten.) Whatever the reason for the oversight, given our ignorance on the subject there is little doubt that the interaction patterns and exchanges of rewards that develop in organizations would stand out more clearly if sexual differentiation were taken into account. With this in mind, we have investigated patterns of sexual differentiation in five small, highly professionalized organizations. Information from these organizations was used previously to explore the social-psychological implications of Weber's model of bureaucracy (Miller and Fry), but this is the first time that the possibility of sexual inequities has been directly investigated. The research proceeded in two stages. First, the differences between men and women in three areas of organizational activity were determined: 1. differences in access to organizational networks of interaction were examined, using sociometric measures of interpersonal attractiveness (specifically, friendship, perceived influence, professional respect and or*This research was sponsored in part by NIMH grant no. 23274-01 Al and by the Social Sciences Research Institute of the University of Southern California. We are grateful to Steven Bloch for his assistance in the analysis of the data, and to our colleagues, too numerous to Iist, for their perceptive comments on early versions of the paper.