Respiration rates have been determined of potatoes grown under varying nutritional conditions. Intact tubers as well as tissue disks were used in these experiments. No effect of magnesium supply on respiration rate was found. Tubers and tuber disks from nitrogen-deficient and those from phosphorusdeficient plants had in some cases somewhat lower respiration rates than those from fully manured plants. Potassium-deficient tubers were found to have considerably higher respiration rates than tubers grown on the same field at an optimum K-supply. This difference was shown to be due to a different sensitivity to bruising of K-deficient and of normal tubers. The effect of bruising on respiration rate was assumed to be identical with the wound effect as it was found in tuber disks. Some evidence was obtained that the wound effect depends on increased activity of potato protein after wounding. No effect of potassium supply on cell respiration has been observed. In experiments with copper-deficient potatoes evidence was obtained that tyrosinase does not function as the terminal oxidase in the respiration of the tubers.