I examined the short- and long-term low-temperature tolerance of American plaiceHippoglossoides platessoides, a coldwater flatfish species, in an attempt to relate temperature tolerance in the laboratory to declines in the species' abundance following years with unusually cold water temperatures. American plaice were very tolerant of rapid declines in temperature over 96 h, and no fish died when placed in temperatures of less than –1.30°C until acclimation temperatures were above 10°C. They also survived 77 d at –1.40°C; although they were more active at that temperature than fish at 0.18°C, they did not eat, and they lost weight. The observed declines in population biomass may have been caused by starvation rather than by cold itself.