The extinction performances of groups of Cercopithecus and Lemur were compared subsequent to criterional training and to 100 reinforcements with two projected problems in a totally automated situation. On the assumption that rate of extinction might be a positive correlate of discrimination learning, it was predicted that Cercopithecus would extinguish more rapidly than Lemur for its discrimination-reversal (DR) skills were known to be superior. This prediction was confirmed. Cercopithecus in contrast to Lemur also tended to shift in choice from the stimulus that was correct in training, & point consistent with its superior DR skills. Only with regard to daily performance expressed as a proportion of total responses emitted during extinction were the patterns of extinction the same for the two groups.