Spleen and thymus weight, delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC), contact hypersensitivity to picryl chloride, anti-sheep red blood cell hemagglutinin titers and plaque-forming cells (PFC), resistance against experimental toxoplasmosis as well as serum total and intestinal specific IgA were investigated in Swiss mice given sodium valproate (250 mg/kg/day) orally for 21 consecutive days. Sodium valproate (SV) did not exert marked effects as only DTH to SRBC and PFC numbers were found to be slightly altered. These results suggest that SV is unlikely to alter immune competence markedly.