A comparison of the amt. of citrate accumulating in the tissues of normal and X-irradiated animals after fluoroacetate treatment indicated that X-ray markedly inhibits citrate synthesis in some tissues. After 800 r of X-ray, citrate accumulation was markedly inhibited in spleen, thymus, ileum and pancreas while kidney, testes, and skeletal muscle showed some inhibition. No inhibitory effects were observed in heart and brain. Sublethal doses (100-400 r) markedly inhibited citrate synthesis in spleen and thymus. The extent of inhibition was dependent upon the dose of X-ray and was reversible after sublethal doses and irreversible when lethal doses were given. These expts. demonstrated that some reaction involved in citrate synthesis in radiosensitive tissues is markedly inhibited by X-ray. In contrast to results obtained with other tissues an increase in the citrate content of liver tissue from male rats occurred after X-ray and fluoroacetate treatment. Unirradiated female rats accumulated citrate in the liver to about the same extent as irradiated male rats. These results indicated that the sex hormones normally regulate citrate synthesis in the liver and that X-ray alters this regulatory effect probably through inhibiting androgen synthesis.