Utilizing an adherence separation procedure, marrow cells from six neutropenic patients were studied in cell culture for colony-forming ability (CFU-C), and for colony-stimulating function of the adherent cell (A-C) population. Assays on two patients showed reduced CFU-C and A-C function, while assays on three patients yielded normal CFU-C and A-C function; studies on the remaining patient exhibited reduced CFU-C in the presence of normal A-C function. The demonstration of these various abnormalities in marrow cell culture from neutropenic patients suggests that the in vitro techniques have relevance to the study of granulopoiesis in vivo.