The relationship of group size to vicarious reinforcement (VR) was investigated under conditions controlled either for number or percentage of reinforced responses heard by Ss in simulated groups. The effect of adding direct reinforcement (DR) to the observing S was examined at each level of group size. In a modified verbal conditoning task, with "Good" as reinforcer and Humans as critical class, Ss said words intermittently with ape recorded voices. It was found that decreasing proportion of reinforced vicarious responses by increasing group size resulted in significantly lower learning. When number of reinforcements increased (proportion held constant), learning curves did not differ. Adding DR to VR did not significantly increase learning at any level of group size. (PsycINFO Database Record (c) 2006 APA, all rights reserved)