It has been found that administering rabbit anti-bursa serum (ABS) to chickens, like neonatal bursectomy, brings about a decreased acid phosphatase (APh) reaction in germinal centres type I and II, and in the periellipsoidal lymphatic tissue (PEL) of the spleen. It has turned out, that following a stimulation with sheep erythrocytes (SRBC) in the blood serum of the ABS-treated chickens appear traces of specific anti-SRBC agglutinins, while in bursectomized chickens there is only a slight decrease in the titre of those antibodies. The results may serve as a base for further studies on the role and participation of the spleen structures in chicken immunological response.