A laboratoryexperiment was conducted to study the effects of two types of anonymityin an electronic meeting system (EMS) setting (source anonymity: participants know who their group members are but do not know the source of any comment, and participant anonymity:, participants do not know who their group members are), initial difference in opinions, and their interaction on participation and satisfaction. Results suggest that the effects of participant anonymityshould not be considered as similar in nature to but stronger than those of source anonymity. The extent to which source and participant anonymitymake a group salient to its members is proposed as a crucial determinant of the effects of source and participant anonymity.