During exposure to the leukoattractant FMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine) human polymorphonuclear leukocytes (PMNL) exhibit a bimodal pattern of luminol-enhanced chemiluminescence (LECL) with distinct early extracellular and later-occurring intracellular membrane-associated oxidative responses [4, 7, 14]. With the primary objective of measuring the effects of oral administration of the antioxidant ascorbate on the generation of reactive oxidants by circulating phagocytes from cigarette smokers and nonsmokers, we have developed a method for the measurement of FMLP-activated LECL in whole blood. With this method definite bimodal LECL responses, similar to those obtained with pure PMNL, were observed with FMLP-activated whole blood. No LECL responses were observed when whole blood from 3 children with chronic granulomatous disease was stimulated with FMLP, which shows that the FMLP-activated LECL responses are exclusively phagocyte-derived in blood from normal individuals. The whole blood method was used to compare the FMLP-activated LECL responses in blood from 30 asymptomatic smokers and 30 nonsmokers and to investigate the effects of co-incubation of whole blood from smokers and nonsmokers with ascorbate (2.5 X 10(-5) M-2.5 X 10(-4)M), as well as the effects of oral administration of the antioxidant on FMLP-activated LECL. Increased generation of both extracellular (58% mean increase, P less than 0.005) and intracellular (75% mean increase, P less than 0.005) phagocyte-derived oxidants was observed with FMLP-activated blood from smokers relative to nonsmokers. Co-incubation of blood with ascorbate in vitro caused a dose-dependent selective neutralization of extracellular oxidants. Similar effects were observed following the oral administration of a single dose of ascorbate (1 g). The whole blood method may be useful in identifying smokers at risk for smoking-related diseases.