The effect of the supernatants obtained from the liquid culture medium of Sporothrix schenkii and Candida albicans on the generation of superoxide anion (O2- and hydroxyl radicals OH., the elements of reactive oxygen species (ROS), and chemoluminescence (CL), a measure of several ROS, by polymorphonuclear leukocytes (PMNs) was examined. In our study, it was shown that the supernatant of S. schenkii increased all types of ROS generation examined and CL, while that of C. albicans increased OH. generation and CL. The effect of the supernatants of S. schenkii on OH. generation and CL and that of C. albicans on CL were most remarkable when the supernatant obtained 8 weeks after the inoculation was used. The supernatant of S. schenkii was shown to be a much more potent stimulant than the supernatant of C. albicans. This ROS-stimulating effect of the supernatant of S. schenkii was heat stable but not dialyzable. These findings suggest the possible role of ROS produced by infiltrated PMNs in the inflammatory skin lesions induced by S. schenkii.