Only high levels of anesthetics and long times of exposure cause significant histotoxicity in laboratory studies on cells and animals. The disease-provoking mechanism involves profound physiological phenomena associated with anesthesia. Trace concentrations of anesthetics produce none of these effects. Therefore, studies using high concentrations have no value in predicting the effects of trace concentrations. Laboratory studies show that none of the most commonly used halogenated anesthetics produces cancer in animals. Epidemiological studies show no correlation between anesthetics and cancer in men and only a dubious correlation in women. The epidemiological studies to date on reproductive disease are inconclusive. They have not been designed to eliminate errors of data gathering or statistics. Nor have they been designed to test the cause-effect relationship between trace concentrations of anesthetics and reproductive disease. Anesthesiologists have a lower mortality rate than physicians as a whole. Conservative environmental health standards suggest that anesthetic levels in excess of those found in unscavenged operating rooms should be nontoxic. There are no statistically sound studies which prove that trace concentrations of anesthetic gases exert harmful effects.