Surveillance was done on cancers in subjects in rural Iowa for 6 years after they participated in a cardiovascular risk factor-screening program. Among 5,565 men and women 20-94 years old at screening, 131 persons were identified as having cancers. Each cancer patient was matched to a control without cancer, and differences in antecedent plasma cholesterol and triglyceride levels and relative weight were sought. Mean relative weight at screening was lower among cancer patients of both sexes than among controls. Plasma cholesterol levels were lower among male patients and higher among female patients than among controls, with the differences more prominent for those less than 60 years old at screening. In males, the lower cholesterol levels occurred only in those with neoplasms developing within 24 months of screening. The higher cholesterol levels among female patients with cancers limited to gonadal hormone-related sites were not time-dependent. Triglyceride levels were not significantly different between cancer patients and controls in any analytic group, but triglyceride levels did closely parallel cholesterol alterations. A minimum of 1% of the cohort had diagnosed cancers before the screening program.