Leukocytes from 200 mentally ill patients and 100 normal controls were analyzed for electrophoretic variants of arylsulfatase A. Four different variant forms were found in 15 subjects. There is a relatively high occurrence of the arylsulfatase A variants in patients with alcoholism. Twenty-one per cent (12/56) of patients with alcoholism have a variant enzyme. Only one of the 100 normal controls has a variant enzyme. (This single subject was considered normal by the criteria of the study, namely, a self-report of no current medical problem or psychiatric history. However, upon further testing, it was found that this subject has neurological and neuropsychological deficits). The hypothesis is presented that chronic alcohol intake and abnormal arylsulfatase A act in concert to elevate sulfatide levels which results in abnormalities of brain function. If this hypothesis is correct, persons in whom abnormal arylsulfatase A is expressed may be at risk to the neuropathological effects of alcohol.