Abstract 1. 1.|Echidnas do not sweat, pant, or lick in response to high ambient temperature ( T a ) Platypus produce copious sweat, presumably under adrenergic control. 2. 2.|At a thermoneutral T a (25°C) echidna body temperature ( T b ) is 32.2 C. When T a rises above this level, T b invariably rises, and T b levels above 38°C are generally lethal. 3. 3.|At normal T b 32°C the oxygen consumption of echidnas is about 33% of that predicted for eutherian mammals. When echidna T b is experimentally raised to eutherian level (38°C), the oxygen consumption is 70% of that predicted for eutherian mammals.