Previous research has demonstrated that the difference between a group's potential and its actual productivity is, in part, a function of individuals exerting less effort when working as a team. This phenomenon has been labeled social loafing. Harkins and Petty (1982) have suggested that the way in which teammates think their outputs are combined to make up the team score and teammate competence may influence the social loafing effect. The purpose of this study was to examine the effects of additive, disjunctive, and conjunctive task structures on individual effort expended by rowers and nonrowers. In Experiment 1, 30 male nonrowers were assigned to dyads and performed two (alone, team) 45-sec trials on Concept II rowing ergometers. Ten subjects performed under additive, 10 under disjunctive, and 10 under conjunctive task conditions. Results demonstrated no significant effects. In Experiment 2, 30 subjects were assigned to 15 dyads with the restriction that 1 member of each dyad be a collegiate rower and 1 be a nonrower. The results revealed (a) that rowers expended more effort than nonrowers and (b) a social loafing effect for the least proficient teammate.