Sera from patients with chronic renal failure (CRF) contain a factor(s) which enhances the oxidative metabolism of polymorphonuclear leukocytes (PMN) as assessed by chemiluminescence (CL), superoxide anion generation, and hexose monophosphate shunt activity. PMN oxidative metabolic activity was higher in CRF sera than in sera from hospitalized patients with normal renal function or in sera from normal healthy subjects. The enhancement occurred regardless of whether PMN were unstimulated or were stimulated by a nonspecific soluble membrane stimulant (phorbol myristate acetate), or by opsonized Candida albicans. The enhanced CL was significantly reduced in their sera after normal renal function was restored with successful renal transplantation. This CL-enhancing factor was also detected in dialysate fluids from CRF patients and in urine from normal healthy subjects. When serum, urine, dialysate fluids of these CRF patients were fractionated by Sephadex G-25 column chromatography, the specific fraction responsible for enhanced CL was found in the molecular weight range less than 1,000 daltons, and is an ethanol extractable substance with natural fluorescence. Our findings suggest that the enhanced PMN stimulatory activity in CRF serum is specifically associated with renal dysfunction and can be useful, along with other conventional parameters, for monitoring the progression of CRF.