Chronic granulomatous disease (CGD) results from defects in the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, central to which is the membrane-bound cytochrome b-245. The cytochrome is composed of two protein subunits, the larger (gp91-phox) being deficient in X-linked CGD. In this study, we have analyzed expression of the cytochrome subunits in B-cell lines from two autosomal CGD patients for whom the disease is caused by deficiency of p22-phox, the smaller subunit. We report the presence of a 65-kD precursor of gp91-phox in the membrane fraction of both p22-phox-deficient cell lines, corresponding to the core protein with N-linked carbohydrate side chains in the high mannose form. Expression of p22-phox in these cells resulted in functional correction of NADPH oxidase. In addition, gp91-phox in the reconstituted cells was processed to its terminally glycosylated form. These data suggest that the association of the 65-kD gp91-phox precursor with p22-phox is a prerequisite for processing of the carbohydrate side chains to the complex form in the Golgi. The detection of this precursor will enable characterization of mutations disrupting the subunit interaction (either naturally occurring or derived by in vitro mutagenesis) and so aid in structure-function analysis of cytochrome b-245. Reconstitution of p22-phox-deficient cells shows the potential of gene therapy for this autosomal form of CGD.