The continuation of a study of 24 dogs in the stages of avoidance reacquisition, differentiation training and generalization testing is reported. Subjects had previously received avoidance training with either response contingent CS termination on all trials or on only 50 percent of the training trials, prior to the administration of medial or lateral prefrontal lesions in 16 subjects. The remaining 8 subjects served as nonoperated controls. Following the appropriate surgical treatment, subjects were tested twice for generalization along the tonal frequency dimension of the avoidance CS. Trials to reacquisition criterion were comparable among all dogs, and subjects trained earlier with continuous response contingent CS termination had overlall faster response latencies, except for the medial subject that were slower than subjects trained under the partial schedule. Differentiation performance tended to show more success in the group given the earlier continuous response contingent avoidance training, although data from both training groups were variable. Subjects trained with the partial schedule had more extra- and intertial responses, which are considered as a byproduct of residual fear. Systematic effects from the surgical treatments were not found during differentiation training. Stimulus control by tonal frequency was more pronounced in subjects that had received the partial training schedule, and frequency generalization was disrupted by the lesion effects. The data are considered in light of reinforcement determinates from CS prolongation in the modification of defensive reflex control.