Salivary gland homogenates of the adult female mosquito Anopheles albimanus, but not those of Aedes aegypti, induced light production in the presence of NADPH and luminol, indicating a NADPH oxidase activity producing reactive oxygen species (superoxide anion) by the anopheline salivary homogenate. Superoxide production by the anopheline salivary homogenate was also confirmed by the NADPH-dependent, superoxide dismutase inhibitable, reduction of cytochrome c. The NADPH oxidase reaction measured by light production in the presence of luminol was inhibited by superoxide dismutase and catalase. Both NADH and NADPH were substrates for the production of oxygen reactive species by the salivary homogenate. Activity, as measured by luminol-dependent light emission, was enhanced one order of magnitude in the presence of 1.6 mg/ml of either phosphatidylserine or bovine serum albumin. Molecular sieving and hydroxyapatite chromatography of the salivary homogenate showed coelution of the NADPH oxidase activity with the previously reported salivary peroxidase activity. It is suggested that the salivary peroxidase of Anopheles albimanus has the ability of producing superoxide in the presence of NADPH, and this may provide the peroxidase with substrates necessary for peroxidation of vasoconstrictor amines such as serotonin, released by aggregating platelets at the site of mosquito probing and feeding.