A histochemical study of the renal interstitial cells demonstrates the absence of two of the principal enzymes involved in the citric acid cycle, the cells thus seem to lack the ability to break down fatty acids. On the other hand the renal interstitial cells demonstrate enzyme activity which could be indirect evidence of fatty acid synthesis. A pronounced nodular acid phosphatase activity and unspecific esterase activity were noticed as well as an uniform cytoplasmic esterase activity.