Five hundred consecutive healthy blood donors were tested for serum alanine aminotransferase (ALT) and 44 (8.8%) had increased levels. Donors with and without raised ALT were compared in several aspects but only weight (expressed as percentage of ideal body weight) and sex differed significantly (119.1 ± 14.5 and 106.3 ± 12.8%, respectively; p<0.001 and males 97.7 and 77.1%, respectively; p<0.01). The 44 donors with raised ALT were followed up and in 13 out of 15 donors with persistently raised ALT without obvious reason, a liver biopsy was performed. Ten donors had various degrees of liver steatosis, 2 had normal liver morphology and in 1 donor chronic hepatitis could not be ruled out. If ALT screening is introduced as a surrogate test for non-A, non-B hepatitis in Swedish blood donors, we suggest that a correction for overweight must be considered in order to minimize donor loss.