Summary: Injection of 0.63 mg 19-nortestosterone into eggs prevents differentiation of the bursa Fabricii. Chickens resulting from such treatment were unable to produce precipitins when challenged with a single intravenous injection of BSA at 6 or 22 weeks of age. Chickens surgically bursectomized at 1 and 2 weeks of age along with intact controls were challenged with BSA at 6 and 12 weeks of age. Antibody response of the bursectomized groups was significantly lower than the control group. The responses of age did not differ from one another. Chickens bursectomized at 1, 5 and 10 weeks of age were injected with BSA at 22 weeks of age and were reinjected at 34 weeks of age. The response of chickens bursectomized at 1 week of age was significantly less than the control response, whereas bursectomy at 10 weeks of age had little or no effect on the response at 22 or 34 weeks of age. Bursectomy at 5 weeks appeared to decrease antibody production at 22 weeks but was without apparent effect at 34 weeks. Surgical bursectomy had no effect on body weight. The hormonal injection of the incubating eggs produced birds weighing less than the controls and in generally poor health. Mortality in the hormone treated birds was high.