In the present study, red blood cells from each of the following species,rabbit,goat, sheep, cattle, swine, goose and duck were used as antigen to immunizechicks, and the humoral immune response determined by a direct micro-haemag-glutination test.Goose red blood cells(GRBC) elicited antibodies which gave aclear-cut and strong antibody reaction, and thus was chosen as the indicatorsystem.Chicks were inoculated with GRBC at 7 and 14 days of age respectively toassess the immunological responsiveness of the birds exposed at the age of oneday to (1) infectious bursal disease (IBD) virus and vaccine, (2) Marek'sdisease (MD) virus, and (8) Herpesvirus of turkey (HVT) vaccine.The results showed that the IBD-PBG98 strain produced no immunosuppression,the IBD-virulent strain led to serious immunodepressive effect. The MD virusand HVT vaccine significantly affected the production of haemagglutinatingantibodies in those birds which were injected with GRBC at 7 days of age.parallel histological examination of the bursa Pabricii revealed changes whichwere in agreement with the above observations. However, the neutralizingantibody titres to IBD virus did not show this correlation.This study demonstrated that the GRBC indicator system for evaluating humoralimmune response in chicks was simple, effective and easy to popularize.