Chronic hypoxia tolerance of Thais haemastoma was inversely related to acclimation temperature but not to salinity. Oxyregulatory ability varied inversely with temperature and did not exhibit acclimation after 28 days' exposure to 53 mm Hg O₂. The oxygen consumption rate was lower after 28 days' exposure to hypoxia than under normoxia at 20 and 30 C but was low at all PO₂'S at 10 C. Pyruvate oxidoreductase enzymes were not induced in foot tissue after 28 days' exposure to 10%-67% of normoxia. Activity ratios of alanopine dehydrogenase:lactate dehydrogenase:strombine dehydrogenase:octopine dehydrogenase were 3.8:1.2:1.0:0. Alanopine dehydrogenase activity increased on exposure to anoxia but had returned to control activity by day 2; no change occurred in the other pyruvate oxidoreductase activities over 6 days' exposure. Adenylate energy charge (AEC) was reduced at low PO₂'S. Arginine phosphate concentrations were lower in snails exposed to 10%-33% saturation than in those at 67%100%. AEC declined from 0.7...