Various cancer sites have been explored in relation to the risk from environmental exposures. Nitrate levels are often elevated in ground water in agricultural areas. Nitrate is a suspect cancer risk factor but most studies have been ecologic. A case-control study in eastern Nebraska found an increased risk of non-Hodgkin's lymphoma among those who used public water supplies with average nitrate levels of 4 or more milligrams per liter nitrate-nitrogen. Nitrate data from Iowa and Nebraska are currently being linked to residential histories in case-control studies of non-Hodgkin's lymphoma, leukemia, stomach, esophagus, and brain cancer. An ecologic analysis of county cancer mortality rates and drinking water nitrate levels in 11 states is also underway. Chlorination byproducts, unintentional contaminants of drinking water disinfected with chlorine, have long been suspected to increase cancer risk. A case-control study conducted in Iowa found an elevated risk of rectal cancer associated with long-term intake of drinking water containing elevated levels of chlorination byproducts. Bladder cancer showed no overall association with estimates of past exposure to chlorination byproducts. However, among smokers there were increased risks associated with long-term consumption of chlorinated surface water. Indoor radon exposure was not associated with lung cancer risk in a case-control study of non-smoking women in Missouri. A case-control study of Missouri women is analyzing the association of lung cancer with cumulative radon exposure. Other studies have focused on indoor radon exposure from a combined analysis of occupational studies of radon-exposed miners. Case-control studies of breast cancer in Alaska, Mexico, and India are underway to evaluate the association of risk with serum and/or adipose levels of DDT and its metabolites. A case-control study in Michigan found no association between serum PBB levels and breast cancer risk. An analysis of DDT and other organochorines in relation to risk of endometrial cancer is underway using stored serum from a multi center case-control study of endometrial cancer in the United States. Interactive effects of environmental factors with specific genetic polymorphisms are also being evaluated in a case-control study of nasopharyngeal cancer in Taiwan.