This field study used groups performing "sex-neutral" tasks over a six- to fifteen-week period to examine determinants of emergent leadership and leadership effectiveness. The study included 149 subjects in 35 task groups (28 mixed-sex groups, 4 all-male groups, and 3 all-female groups) working in conjunction with personnel management or business policy courses. Data were collected twice during the period for all measures used in predicting the identity and effectiveness of emergent leaders (based on follower perceptions of their sex, physical and interpersonal attractiveness, and the leader's self-described sex-role identity, i.e., masculine, feminine, undifferentiated, or androgynous). The results showed that the leader chosen by group members did not change from Time 1 to Time 2 except in one group (an all-male group). Most of the results were similar between Time 1 and Time 2, and were consistent with predictions made based upon theoretical considerations and previous research. The hypotheses in this study were tested using a combination of statistical techniques. The results supported the major hypotheses of the study. In general, within the total sample, sex did not influence perceptions of an emergent leader. However, within groups, the probability of a female gaining leadership status was dependent upon the relative proportion of females in the group, i.e., at least half or more members had to be female. Female leaders were rated more physically attractive than male leaders. Male leaders received the lowest ratings of physical attractiveness, even lower than male nonleaders. Leaders were rated more interpersonally attractive than nonleaders. Emergent leaders with high ratings of physical and interpersonal attractiveness were also rated higher on effectiveness. Individuals with a self-described "masculine" sex role identity emerged as leaders more than undifferentiated, feminine, or androgynous types. There were no differences in leader effectiveness ratings among the four leader types.