MENDELIAN autosomal inheritance patterns have been demonstrated in familial aggregations of polyposis coli, retinoblastoma, xeroderma pigmentosum, neurofibromatosis,1 Gardner's syndrome2 and the basal cell nevus syndrome.3 In addition, an increased familial incidence of carcinoma of the breast,4 lung,5 stomach and colon,6 and prostate,7 as well as leukemia,8 multiple myeloma,9 Waldenström's macroglobulinemia,10 pheochromocytoma,11 multiple endocrine tumors,12 cerebellar hemangioblastoma,13 and malignant melanoma 14 has 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