Recently we applied case control methods to the investigation of motor neuron disease (MND) with surprising results: MND patients have greater exposure to lead and mercury and drink more milk than either diseased or normal age- and sex-matched control patients. Because of the implications of these findings as possible environmental influences in the pathogenesis of MND, we repeated the earlier study using a larger population and a more standardized interview technique. This time the MND patients reported more exposure to mercury or to the combination mercury or lead than either control group. As adults and at age 18, more MND patients drank in excess of three glasses of milk daily. We conclude that exposure to lead or mercury and excessive milk ingestion are possible antecedent events predisposing to MND.