The value of administration of hyperimmune serum in the control of peste des petits ruminants was investigated in goats at different stages of the disease. A group of the goats was given hyperimmune serum intravenously at the fever stage of temperature of 40.5 degrees C or above; another group showing no elevation of temperature but with other clinical signs of the disease were also given hyperimmune serum. Results indicated that hyperimmune serum was very effective in reversing the process of the disease if administered at the fever stage but not in animals that had progressed past the fever stage. The goats given the hyperimmune serum survived for 10 days before showing evidence of reinfection.