Long-term behavioral effects of chronic exposure to low concentrations of halothane were evaluated in rats exposed to low (12.5 ppm) concentrations from day 2 of conception until either 30 (halothane-30) or 60 (halothane-60) days after birth. Rats similarly treated but not exposed to halothane served as controls. When these rats were tested for radial arm maze exploration as adults (1 yr old) both exposure groups showed significant deficits compared with controls. The halothane-treated rats entered significantly fewer arms before reentering an arm (entries-to-repeat). At 55 days of age, in the spontaneous alternation test, response speed was significantly slower than controls in both halothane-30 and halothane-60 rats. This effect was not seen in rats more than 55 days old. Replicating previous results, the halothane-60 rats showed deficits in learning a light-dark discrimination. This deficit was not seen with halothane-30 rats, indicating that continued halothane exposure during the 30- through 60-day period was necessary for inducing a noticeable long-term learning deficit. The results show that chronic exposure of rats to low concentrations of halothane during development results in subsequent behavioral alteration, and that termination of halothane exposure at 30 days of age rather than at 60 days of age avoids some of the signs of behavioral impairment.