We tested the hypothesis that neutrophils contribute to endotoxin-induced impairment of endothelium-dependent and -independent cyclic guanosine monophosphate (cGMP)-mediated pulmonary vascular smooth muscle relaxation. Rats were studied 6 h after endotoxin (20 mg/kg, intraperitoneal) or saline (1 cc, intraperitoneal). Neutrophil-depleted rats were studied 4 days after administration of vinblastine (750 micrograms/kg, intravenous). Concentration-response curves were generated for acetylcholine and sodium nitroprusside in isolated pulmonary arterial rings (10(-9) M to 10(-6) M). The absolute neutrophil count of controls was 1050 +/- 206 neutrophils/mL, and the absolute neutrophil count of vinblastine-treated rats was 100 +/- 41 neutrophils/mL (p < .05 versus controls) and 25 +/- 25 neutrophils/mL in vinblastine-treated rats receiving endotoxin (p < .05 versus control and endotoxin). Endotoxin-induced impairment of endothelium-dependent and -independent cGMP-mediated pulmonary vasorelaxation was significantly attenuated by prior treatment with vinblastine. We conclude that neutrophils contribute to the pathogenesis of endotoxin-induced impairment of cGMP-mediated pulmonary vascular smooth muscle relaxation.