The metabolism of the Antarctic brachiopod Liothyrella uva (Jackson, 1912) has been investigated in the laboratory under simulated winter conditions of low temperature and no food. Under such conditions the metabolic rate measured should approximate to basal or maintenance metabolism. The oxygen consumption of a brachiopod of 35 mm length (210 mg AFDW) was 0.48 μg-at. O · h−1. This is low when compared with other brachiopods, Antarctic invertebrates or starved temperate invertebrates. Ammonia excretion was also low, 0.056 μg-at. NH3-N · h−1 in a 35-mm animal. The slopes of the allometric relationships against ash-free dry weight were 0.72 for oxygen consumption and 0.75 for ammonia excretion. These slopes were not significantly different from each other, or from 0.75. The mean overall oxygen: nitrogen ratio was 9.3, which suggests that protein was being used as the main metabolic substrate. A preliminary biochemical study of brachiopods collected from Signy Island, Antarctica, showed only small seasonal changes in lipid and carbohydrate, but there were marked changes in protein content in the later stages of winter. This confirms that, at least in late winter, L. uva survives primarily by the utilization of protein.