The immune system has been previously demonstrated to be under the influence of maternal nutrition in pregnancy. Assessment was made of the effects of low protein diets (12, 9 and 6 g casein/100 g diet) fed before conception and during pregnancy on the immune system of the resulting offspring in early adulthood. Control animals were fed a diet containing 18 g casein/100 g. At the end of pregnancy all dams were fed a nonpurified diet containing 18.3 g protein/100 g. Male pups were weaned onto this diet, which they consumed until the age of 7 wk. Rats exposed to 18 g casein/100 g diet in utero mounted a typical acute phase response following E. coli endotoxin challenge at age 7 wk. Food intake was 75% lower, hepatic zinc concentrations 25% greater, and serum albumin 15% lower than in saline-injected controls. Pulmonary glutathione levels were 35% greater in endotoxin-treated rats than in saline-treated controls. In rats exposed to low protein diets in utero the trend was for the acute phase response to be blunted. This was most noticeable with respect to the anorectic response, hepatic zinc uptake and pulmonary glutathione uptake. In rats not challenged with endotoxin, maternal diet had pronounced effects on tissue zinc status at the age of 7 wk. Liver zinc concentrations were 21% and 16% lower in the groups exposed to 9 and 6 g casein/100 g diets relative to the control group exposed to 18 g casein/100 g diet. Glutathione status was altered in all groups exposed to low dietary protein in utero.(ABSTRACT TRUNCATED AT 250 WORDS)