This study will look for links between corn farming practices and short-term changes in immune function in farmers throughout the growing season. It will examine biologic effects associated with specific pesticide exposures and general planting activities, such as tillage. Farmers have an increased risk of non-Hodgkin's lymphoma and certain other blood cancers such as multiple myeloma and leukemia, but the reasons for this increase have not been identified.

Findings of this study may contribute to learning the causes of cancers such as non-Hodgkin's lymphoma.

Farmers enrolled in the Agricultural Health Study (a study of pesticide applicators and their spouses in Iowa and North Carolina) and a group of control subjects selected from agricultural extension workers in Iowa may participate in this study.

The study involves six home visits to farmers and four visits to farmers to individuals in the control group. All participants will complete the following tests and procedures:

• Questionnaires and diaries - During the first visit, all participants will have a medical history review, including questions about smoking and other health habits. Farmers will be asked about their farming practices, and controls will be asked about their occupations. Farmers will fill out daily diaries during short time periods of interest around certain pesticide applications to describe farming activities that day. At other times during the growing season before harvest, farmers will fill out weekly diaries describing farming activities; controls, meanwhile, will fill out weekly diaries describing their health and work activities. At home visits during the farmers' growing season, all participants will fill out questionnaires about their health. Finally, farmers and controls will complete a more extensive questionnaire in the off-season, during the last home visit, to learn about their activities and exposures in the final part of the year (post-harvest for farmers).
• Urine samples: At the time of each home visit, controls will provide a urine sample that the interviewer will take that day. Farmers, too, will provide urine samples at the time of home visits, but they will also collect urine samples for a period of 4 days each during short time periods of interest after certain pesticide applications. The interviewer will collect these samples immediately at the end of these periods.
• Blood samples: At the time of each home visit, the interviewer will draw 50 ml (3.5 tablespoons) of blood.
• Telephone calls: Farmers will be called frequently-from once every 2 weeks to every other day-to schedule visits at the times of interest. Control subjects will also be called frequently to schedule their visits closely to those of the farmers.