1. The urine compositions of the European mole Talpa europaea and of the white rat Rattus norvegicus (albino) kept on a carnivore's diet were compared. 2. The urine of moles contained bicarbonate while that of rats kept on a carnivore's diet did not. 3. Urine volume per 100 g body mass over 24 hr was significantly higher in the mole than in the rat. 4. The results of this study suggest that the mole, like other subterranean mammals on the one hand and caecal fermenters on the other, may use its kidneys as a pathway for releasing bicarbonate in its hypercapnic environment.