MENDELIAN autosomal inheritance patterns have been demonstrated in familial aggregations of polyposis coli, retinoblastoma, xeroderma pigmentosum, neurofibromatosis,1Gardner's syndrome2and the basal cell nevus syndrome.3In addition, an increased familial incidence of carcinoma of the breast,4lung,5stomach and colon,6and prostate,7as well as leukemia,8multiple myeloma,9Waldenström's macroglobulinemia,10pheochromocytoma,11multiple endocrine tumors,12cerebellar hemangioblastoma,13and malignant melanoma14has been observed. However, the mode of inheritance is not clear in these latter conditions. In appraising these data, it must be kept in mind that only those families showing a high incidence of carcinoma are "selected" for publication. When one considers the high population incidence of carcinoma, "... it is bound to occur in excess in some families according to the operation of the laws of probability.15" The purpose of this paper is to present the findings in two large midwestern kindreds in which a high frequency of