Respiratory rates ofMacoma balthica, Mulinia lateralis andMya arenaria were determined under an experimental design using acclimation and exposure temperatures ranging from 1 to 30 C. Rates decreased with increasing size and in general varied directly with temperature. However, high temperatures (30 C) depressed metabolism of cold-acclimatedMulinia andMya. Very youngMya were less affected by high temperature (30 C) than wereMya a few months older.Mya andMulinia demonstrated acclimation pattern III A. SmallMacoma had pattern III B, which changed to IV C for larger animals. Macoma was least affected by high or low temperature stress, followed byMya, thenMulinia. All three species were able to compensate for temperature change to a varying extent. Unseasonal artificial warming of the benthic environment could elevate metabolism of the species studied, which could lead to starvation if food were scarce, especially in winter.