The objectives of this study were to determine the effect ofzinc deficiency on blood pressure in immature rats and to determine if high levels of dietary calcium influence the response. Weanling male albino rats were fed for 26 days diets based on soybean protein and egg white and containing either 0.65% or 2.0% calcium. Within each Ca series two groups consumed a low-zinc (<1 ppm) diet, ad libitum or paired-fed, and two consumed a zinc-adequate (50 ppm) diet, ad libitum or paired-fed. Serum zinc and angiotensin converting enzyme activity were significantly reduced by zinc deficiency but these parameters were unaffected by dietary calcium. Zinc deficiency lowered the direct blood pressure 27 mm Hg in anesthetized rats; compared to controls there was no effect of dietary calcium. Zinc deficiency also increased serum magnesium. These data suggest that reduced blood pressure in zinc deficient rats depends on the severity of the deficiency and not on the dietary calcium level.