The need for effective, safe, specific cellular immune suppression in avian research led to the study of effects of tilorone and niridazole on cell-mediated immunity of chickens. Two in vivo tests for cell-mediated immunity function were used--the graft-vs-host (GvH) test and the delayed hypersensitivity (DH) test. Humoral immunity was evaluated by measuring natural hemagglutination (HA) titers against rabbit red blood cells. Intraperitoneal administration of tilorone to young chickens appeared to have severe toxic side effects and was of little value as an immune suppressant. Oral administration of tilorone to 6-week-old chickens caused DH suppression, but no marked effect was seen on GvH reactions or HA titers. Toxicosis appeared less severe. Oral administration of niridazole to 6-week-old birds caused nearly complete loss of GvH and DH reactivity but caused an increase in HA titers. General toxic effects of niridazole were not apparent.