Male Sprague-Dawley rats were exposed to chlorine-based disinfectants in the drinking water from weaning to 12 weeks of age, at which time they were terminated and assessed for immune competence. Chlorine-based drinking water disinfectants used were sodium hypochlorite (5, 15 and 30 ppm) and monochloramine (9, 19 and 38 ppm). Significant (P < 0.05) reductions of spleen weight, delayed-type hypersensitivity (DTH) reactions, and oxidative metabolism by macrophages were observed only in groups of rats exposed to high levels (30 ppm) of sodium hypochlorite, while prostaglandin E2 (PGE 2) production was elevated. Rats exposed to the higher doses of monochloramine had reduced spleen weights (38 ppm), decreased antibody synthesis (9 and 19 ppm) and augmented PGE 2 production (19 and 38 ppm). Alteration of immune function of chlorine-based disinfectant-exposed rats in the study was only evident at relatively high doses, and only selected immune responses were altered; therefore, it appears that these chlorine-based disinfectants are not particularly strong immunodepressants. (Copyright (c) 1987 Elsevier Scientific Publishers Ireland Ltd.)