Ventilation rates and oxygen consumption rates of the bay scallop, Argopecten irradians, were monitored for periods of 28 to 72 hours at temperatures of 10, 15 and 29°C. The scallops were placed in a Brett-type swimming speed respirometer.  This allowed the simultaneous monitoring of ventilation rate and oxygen consumption.  Mean ventilation rates for all scallops at the three temperatures were: 0.55 L/animal hour at 10°C, 0.51 L/animal hour at 15°Celsius, and 1.28 L/animal hour at 20°C, while mean oxygen consumption rates were: 0.0375 ml 02 /hr/gm wet weight at 10°Celsius, 0.1717 ml 02 /hr/gm wet weight at 15°C, and 0.2427 ml 02 /hr/gm wet weight at 20°C. The ratio of ventilation rate to oxygen consumption was determined at each temperature to give an indication of feeding efficiency.  At 10°C the scallops pumped 14 L/ml 02 consumed, at 15°Celsius they pumped 3L/ml 0 2 consumed, and at 20°Celsius they pumped 5.3 L/ml 02 consumed.  Oxygen consumption was quite uniform during the experimental runs.  Scalloped at all temperatures tested were able to bring the oxygen tension down to 0.2 ppm and recover when placed in a tank of aerated water.  During the experimental runs it was noted that the fluorescence of the algae exhibited circadian rhythms.