Specimen Collection for Agricultural Health Study Cohort Pesticide Exposure Study

Background: \- Multiple myeloma (MM), a type of cancer that affects the white blood cells, is often preceded by a precancerous disorder known as monoclonal gammopathy of undetermined significance (MGUS). Farmers and other agricultural workers have a higher risk of developing MGUS and MM, possibly because of their exposure to certain pesticides. Researchers are interested in studying biological specimens taken from participants in the Agricultural Health Study - specifically, pesticide applicators at least 50 years of age who do not have cancer- to better understand the development of MGUS and MM. Objectives: * To collect biological specimens from Agricultural Health Study participants for further research. * To examine the relationship between pesticide exposure and MGUS/MM. Eligibility: \- Male pesticide applicators who are over 50 years of age, cancer-free, and participating in the Agricultural Health Study. Design: * Two groups of participants will complete the study: a general group and a smaller group of individuals who have been exposed to the pesticide diazinon. * All participants will receive an initial contact letter with information about the study, followed by a phone call to administer a screening questionnaire and arrange a home visit from a researcher within the next month. * Participants will receive by mail a urine specimen kit that will be collected at the home visit. * During the home visit, a study researcher will take blood samples and collect the urine sample, and will administer another questionnaire. * Participants in the group exposed to diazinon will have three home visits for the study: (1) prior to pesticide exposure, (2) the day after participants stop using diazinon, and (3) about 21 days after the second visit. The first visit will take place in the off-season from January to March; the second and third visits will be conducted between April and August. * No treatment will be provided as part of this study.