Three species of the marine wood-boring genus Limnoria were subjected to low dissolved oxygen concentrations at different temperatures under laboratory conditions. 28-day median tolerance limits (TLm) were 1.0 mg/l of dissolved oxygen at 15° to 16°C and 19° to 20°C for L. lignorum, 0.75 and 0.60 mg/l at 15° to 16°C and 22° to 25°C, respectively, for L. quadripunctata, and 1.0 and 1.18 mg/l at 15° to 16°C and 22° to 25°C, respectively, for L. tripunctata. The amount of burrowing activity, as measured by the egestion rate, was directly related to the amount of dissolved oxygen. A daily egestion rate of 0.116 mg per day in L. tripunctata at 22° to 25°C was the highest figure measured. The daily egestion rate was sharply reduced at dissolved oxygen concentrations below 3.0 mg/l