A laboratory experiment investigated the effects of physical group size (five- and ten-member) and logical group size (i.e., group heterogeneity in regard to task demands) on the performance of groups addressing an idea generation task. Logical size was manipulated by varying the amount of task-relevant information given to each group member. Larger logical group sizes (heterogeneous groups) were induced by distributing unique task-relevant information among group members; smaller logical group sizes were induced by providing all task information to all members (homogeneous groups). Ten-member groups outperformed five-member groups. Physical group size interacted with logical group size resulting in greater performance gains for heterogenous groups with more members. Average contributions per group member diminished with increased physical group size for homogeneous groups and increased for heterogeneous groups.