The hypothesis that intragastric synthesis of N-nitroso compounds (NOC) in early life could play a role in gastric carcinogenesis was tested by applying the N-nitrosoproline (NPRO) test to about 50 children living in high- and low-risk areas for stomach cancer in Costa Rica. The median values of excretion of NPRO and the sum of three nitrosamino acids (micrograms/12 h urine) were 10-20% of those in adults from other geographical high-risk areas for stomach cancer. The urinary NPRO level after proline intake was higher in children from the high-risk area (P < 0.04) and markedly reduced after ingestion of ascorbic acid together with proline (P < 0.05). NPRO levels on the day of proline intake were highly correlated with levels of nitrate excretion (P < 0.001). Mean levels of total NOC in an aqueous (pH 2) extract of cooked beans from the high- and low-risk areas were similar. Acid-catalyzed nitrosation of the extract increased the total NOC concentration up to 1000-fold, but there was no difference between samples from the two areas. About 10% of bean extracts from both areas showed weak direct-acting genotoxicity in Escherichia coli; after acid-catalyzed nitrosation, all samples were genotoxic at similar levels. The diet of children in the low-risk area satisfied recommended levels of intake of energy and most nutrients except riboflavin and retinol equivalents. Diets from the high-risk area were deficient in energy intake and all nutrients except protein and vitamin C.(ABSTRACT TRUNCATED AT 250 WORDS)