In studies of the effect of diet on nitrosamine levels in selected human physiological fluids, volunteers were fed meals containing fish or beef (sources of precursor amines) or bacon (a source of preformed nitrosamines), in combination with spinach and vegetable juice to supply nitrite via possible reduction of nitrate. Blood, urine and gastric contents were sampled periodically for up to 4 hr after feeding. The results of the study indicated that traces of nitrosamines, usually N-nitrosodimethylamine, were present in many samples of blood, urine and gastric contents, even after an 8-hr fast. Eating the test meals led to a slight increase in nitrosamine levels in the blood and stomach contents in a few subjects. The data obtained from this study suggest that gastric formation of nitrosamine does not appear to be an important health factor in normal people, since the levels of nitrosamines found in physiological fluids are not markedly increased after eating.