Several reports in the literature suggest a relationship between lead intoxication and thermoregulatory capacity. To investigate the effects of lead on the control of body temperature, mice of the BALB/c strain were injected intraperitoneally with lead acetate (0 to 100 mg/kg) while colonic temperature was measured 30, 60, and 90 min post-injection at ambient temperatures (Ta) of 20 and 30 C. Lead acetate caused a transient hypothermia, an effect which was augmented at cooler Ta's. In a second experiment, mice were injected with 100 mg/kg lead acetate and placed in a longitudinal temperature gradient to measure their preferred Ta. Lead acetate significantly reduced the preferred Ta during the first 30 min post-injection. Thus, lead acetate-treated mice selected a cooler Ta which augmented the lead-induced hypothermia. In a third experiment it was found that lead acetate-induced lethality was potentiated with increasing Ta. Hence, the hypothermic response to acute lead acetate treatment may be beneficial to survival.