The effects on fertility and reproductive wastage of 110 female Swiss/Webster mice and postnatal survival of their offspring were examined after exposure to either air, 0.4% isoflurane, or 0.1% isoflurane. Treatments were for 4 h daily for 2 weeks before and during pregnancy. In a second experiment, the effects on fertility of 54 male Swiss/Webster mice and on reproductive wastage of their unexposed mates were examined after 4-h daily exposures to either air, 0.4% isoflurane, or 0.1% isoflurane throughout spermatogenesis and during mating. There were no adverse reproductive effects in either experiment. The lack of toxicity of isoflurane is consistent with the results of other reproductive studies in animals that have examined chronic intermittent exposure to subanesthetic concentrations of halothane, enflurane, methoxyflurane, and nitrous oxide. They suggest that these and lower (trace) levels of anesthetic gases may not be the cause of the harmful reproductive effects said to occur in operating room personnel.