Many workers have investigated the possibility that bovine leukemia virus (BLV) might be transmissible to man. The epidemiological studies were designed to examine for associations between human leukemia and a rural environment, cattle farming, veterinary activities, or bovine leukosis. The serological studies were used to test serum samples from human cancer patients and from persons with potential occupational exposure to BLV, among others, for evidence of BLV antibodies. All these studies are critically reviewed. It is concluded that there is no epidemiological or serological evidence from human studies to indicate that BLV can infect man.