Beta-carotene and cancer prevention: the Basel Study. In 1971-1973 at the third examination of the Basel Study started in 1959, the major antioxidant vitamins and carotene were measured in the plasma of 2974 men. A subsample and their families were reinvestigated in 1977-79. During the 12-y observation period (1973-85) 553 men died, 204 of cancer (lung cancer 68, stomach cancer 20; colon cancer 17, all other malignancies 99). We found significantly lower mean carotene levels for all cancer, bronchus cancer, and stomach cancer (all P less than 0.01) compared with the 2421 survivors. The relative risk of subjects with low carotene (less than 0.23 mumol/L) was significantly elevated (P less than 0.05) for lung cancer (Cox's model). Higher risks were noted for all cancer (P less than 0.01) if both carotene and retinol were low. Low plasma carotene which is known to reflect carotene intake is in our study associated with increased cancer risk. 