Multiple myeloma was diagnosed in six residents of Thief River Falls, Minn. in 1968 (a rate of 84/100,000). A survey of the normal population for monoclonal serum protein peaks was undertaken in 1969. Serum from 1200 residents of the city, who were 50 yr of age or older, was collected. Fifteen (1.25%) had monoclonal serum protein peaks: IgG in 11, IgA in one, and IgM in three, with kappa in 11 and lambda in four. No clinical, laboratory, or roentgenographic evidence of myeloma or macroglobulinemia was found in any of the patients. The incidence of monoclonal serum protein peaks is similar to that reported from Sweden. It was concluded that there was no significant increase in monoclonal proteins in the population of Thief River Falls. The 1968 socalled epidemic of multiple myeloma in Thief River Falls remains unexplained.