The relationship between neutrophil function and the neutrophil antigen, Kx, as well as the linkage of the gene, Xk, with Xg was examined in a kindred with X-linked chronic granulomatous disease. Four of the eight male siblings had chronic granulomatous disease by clinical history and tests of neutrophil function, and all four had Kx- negative neutrophils. The remaining four were in good health and had normal nitroblue tetrazolium reduction tests. However, one of these latter four had Kx-negative neutrophils that functioned normally. These data suggest that closely linked but distinct genes on the X chromosome code for chronic granulomatous disease and Kx. In addition, close linkage was demonstrated between Xk and Xg, a gene coding for an erythrocyte surface antigen.