Functional activity (biocidal properties) of whole blood phagocytes from humans exposed to ozone was studied by measuring spontaneous and zymosan-induced luminol-dependent chemiluminescence. Generation of reactive oxygen species and biocidal properties of phagocytes depended on the time of ozone exposure and development of bronchopulmonary diseases. The data suggest that generation of reactive oxygen species must be assayed for elaboration of individual patient management programs.