This experiment was designed to test the motivation to perform a task for males and females in mixed and same-sex groups. Individuals in homogeneous groups (four males or four females) or heterogeneous groups (two males and two females) clapped their hands alone, in pairs and in foursomes. People exerted more effort alone than in groups, regardless of group compositions. Females performed better in same-sex pairs than in opposite-sex pairs. Implications concerning relative abilities and social loafing are discussed. (Author)