Non-Hodgkin's lymphoma (NHL) incidence rates have risen three percent per year in the U.S. for four decades. Mortality from NHL has risen 1.6 percent, compared with 0.2 percent for all cancers combined. This epidemic curve appears in both sexes and around the world, suggesting the possibility of an etiologic agent increasing in prevalence in the general environment. Recent research has identified several possible candidates including pesticides, other organochlorines, drinking water nitrates, and sunlight. There is an urgent need to evaluate whether these common exposures are contributing to the rapid rise in NHL, and to investigate other hypothesized risk factors such as viruses, medical conditions, hair dye use, and genetic factors. The purpose of this study is to examine the contribution to NHL risk of these important environmental, occupational, viral, medical, and personal exposures, and to pursue important leads emerging from on-going NHL research. This multidisciplinary, population-based case-control study will involve personal interviews to collect information on demographics, residential history, pesticide use, and occupational exposures; self-administered questionnaires to collect information on diet, family and medical history, and other exposures; tap water and carpet dust sampling to collect information on nitrate and pesticide exposures; and blood sampling for measurements of compounds in the serum, antibodies to viruses, and examination of genetic polymorphisms.