Rat pups emit ultrasonic vocalizations (USVs) during cold challenge. R. F. Kirby and M. S. Blumberg (1998) suggested that when brown adipose tissue (BAT) thermogenesis fails to compensate for body heat loss and heart rate declines, infant pups maintain venous return to the heart with a mechanical maneuver that is accompanied by ultrasonic emissions. Thus, manipulations that attenuate or enhance BAT thermogenesis should have inverse effects on cold-induced USVs. The authors found that hexamethonium (10 mg/kg) and propranolol (1 and 20 mg/kg) attenuated BAT metabolism while enhancing USV production, and norepinephrine (NE, 800 microg/kg) enhanced BAT metabolism while ultrasonic emissions decreased. The findings are consistent with the hypothesis that BAT metabolism influences USVs during cold challenge by affecting cardiac rate and inducing compensatory, homeostatic responses.