Conditioned flexion reinforced by shock, conditioned flexion reinforced by food, and conditioned salivation reinforced by food were elaborated, each type of response being represented in 1 of 3 groups, each group containing four dogs. Once the frequency of response with consistent reinforcement was established, each type of response was reinforced with the appropriate stimulus 80, 60, 40, and 20% of the time. The frequency of conditioned flexion reinforced by shock does not vary with the frequency of reinforcement. On the other hand there was a progressive decrease in vocal response, diffuse behavior, complication from postural position, and general restlessness as the frequency of shock-reinforcement was decreased. The frequency of conditioned flexion reinforced by food is the same when reinforcement occurs 100, 80, 60, and 40% of the time, but is significantly less at 20% reinforcement than at 100% reinforcement. The frequency and intensity of conditioned salivation reinforced by food do not vary with reinforcement 100, 80, and 60% of the time, but are significantly less than that at 100% reinforcement, when reinforcement is maintained at 40 and 20%. In no case did the frequency of any of the 3 types of conditioned response drop below 80%.