N-Nitroso compounds, known animal carcinogens, are formed endogenously from drinking water and dietary sources of nitrate and nitrite. The authors conducted a population-based case-control study of pancreatic cancer in Iowa to determine whether increased consumption of nitrate and nitrite from drinking water and dietary sources was associated with risk. They linked detailed water source histories to nitrate measurements for Iowa community water supplies. After exclusions for insufficient data, 1,244 controls and 189 pancreatic cancer cases were available for analysis. Among controls, the median average nitrate level (1960-1987) was 1.27 (interquartile range, 0.6-2.8) mg of nitrate nitrogen per liter of water. No association was observed between pancreatic cancer risk and increasing quartiles of the community water supplies' nitrate level. Increasing intake of dietary nitrite from animal sources was associated with an elevated risk of pancreatic cancer among men and women (highest quartile odds ratios = 2.3, 95% confidence interval: 1.1, 5.1, for men and 3.2, 95% confidence interval: 1.6, 6.4, for women). In contrast, dietary nitrate intake showed an inverse association with risk among women and no association among men. This study suggests that long-term exposure to drinking water nitrate at levels below the maximum contaminant level of nitrate nitrogen (10 mg/liter) is not associated with pancreatic cancer; however, the consumption of dietary nitrite from animal products may increase risk.