1. A continuous flow respirometer suitable for measuring oxygen consumption in some small burrowing aquatic animals is described.
2. Rates of oxygen consumption in ammocoetes of the lamprey Ichthyomyzon hubbsi are low, with mean values at 15.5 °C ranging from 38.8 to 97.1 µl/g/h for large (3.44 g) and small (0.14 g) animals respectively.
3. A Q10 of 3.6 was found for medium-size animals (1.18 g) between 3.5 and 22.5 °C.
4. The slope of the logarithmic linear regression relating weight and oxygen consumption was 0.718 at 15.5°C.
5. The rates of oxygen consumption are discussed with respect to the ecology of ammocoetes and compared with those obtained for other lower vertebrates.