Sera from patients with lung cancer and from healthy donors were screened for the presence of aflatoxins. Significant differences in levels of aflatoxins between the two groups were found. Only 1 of the neoplastic patients with aflatoxins in the serum was a smoker. However the percentage of sera from lung cancer containing aflatoxins is not significant enough to provide evidence for a casual relationship between aflatoxins exposure and development of lung cancer in humans.