We studied CGD in a Black family with three children, including a pair of identical twin sisters (10 yr.), DJ and SJ, and brother (13 yr.), BJ. SJ has had recurrent lung, liver abscesses, DJ recurrent pulmonary infections. BJ has always been in good health. DJ, SJ and BJ could not reduce NBT (.04, .03, .03 O.D.). Father (.16) and mother (.12) were normal (.14). Neutrophil auperoxide production was absent in twins (.00, .03, O.D.) and brother (.02). Mother (.13) was intermediate between control (.39), father (.34), and children. HMP activity for twins (31, 101 CPM) and brother (85 CPM) were well below control (1350), mother (1307) and father (1350). Neutrophils of twins and brother killed only 23%, 32% and 16% Staph. aureus after 2 hours (control 83%). Mother and father were normal. All had normal neutrophil MPO staining. Phagocytic neutrophil 02 consumption expressed in nanomoles/min/12×106 cells was DJ (.00), SJ (.01), and BJ (.00). Father (7.3) was normal (5.5). Mother (.77) was very low. Since children of both sex are affected, the mode of inheritance of CGD is not sex-linked. If the mode is autosomal recessive, the apparent absence of neutrophil dysfunction in the father suggests an undetectable carrier state. The unusual severity and frequency of infection in the female twins and the total absence of infection in the brother, a classic CGD, suggest a new variant of this syndrome.