A study was made of respiration and metabolism in Amazonian manatees (Trichechus inunguis) weighing between 20 and 170 kg. These animals had a low metabolic rate, 0.36 times that predicted by Kleiber's 1975 equation for placental mammals. They also had a low breathing frequency and minute ventilation, and high O₂ extraction and CO₂ output. The mean dive times were less than 2 min but dives of up to 10 min-duration were noted. Sequential dive times exhibited a pattern only in that several short dives followed a prolonged one.