Patients with acute leukemia are prone to get infections. Pathological conditions such as leukocytopenia and disturbances of humoral and cellular immunity are thought to contribute to this high susceptibility to infection. Superoxide, one of the active oxygens, is thought to be related to the intracellular bactericidal activities of neutrophils, particularly in oxygen dependent systems. These findings led the author to speculate that primary and secondary disturbances in the superoxide production of neutrophils are of importance in the high susceptibility of patients with acute leukemia. In this experiment, the superoxide production of normal human neutrophils stimulated by Concanavalin A and Cytocharacin D was assayed by spectrophotometer in order to evaluate its usefulness in clinical applications. The effect of age and sex on supreoxide production was also examined. The following results were obtained: 1. The activity of superoxide production was affected by both time and temperature during cell preservation. It was also dependent on the cell concentration, temperature and pH during stimulation of the neutrophils. The optimal system for assay of the superoxide production of human neutrophils was as follow: Cells should be preserved at 0℃ within 60 minutes. During stimulation, cell concentration, temperature and pH should be ajusted to 0.2-0.5x10(6)/ml, 37℃ and 7.4, respectively. 2. There were no significant changes in superoxide production between males and females. Superoxide production in older subjects(70-89 y/o) was significantly lower than that in younger subjects(20-69 y/o)(p<0.001). The values were 4.72±1.17 nmol/min/10(6)-PMNs in the former and 6.45±1.33 nmol/min/10(6)PMNs in the latter. Assays of superoxide production of human neutrophils can be clinically used because of its simplicity and reproducibility. It was apparent that the assessment of superoxide production of neutrophils by age was necessary in clinical applications.