THIS REPORT is on three brothers with chronic lymphocytic leukemia. It is of interest not only because of the rarity of the condition but because the evaluation of heredity in the causation of this disease in man depends upon such families being on record. Reviews of familial leukemia were published by Ardashnikov in 19371 and by Videbaek in 1947.2 The latter compiled, from the literature and his own observations, 82 authenticated cases of leukemia in 37 families. These included four families in which three persons were afflicted and two families with four leukemic members. In this group the disease was found in two or more generations, except for a family originally described by Hornbaker,3 in which two sisters had chronic lymphogenous leukemia and a third sister had chronic myelogenous leukemia. Recently, Anderson4 reported on a remarkable family in which five siblings were afflicted with leukemia. It is believed that the