In adrenalectomized rats, renin substrate was, as previously found, extremely low in non-substituted animals, markedly decreased in salt- substituted animals, but only slightly decreased in both salt- and DOCA-substituted animals. After three of four injuries, known to increase acute phase proteins, there was also an adrenal-dependent increase in renin substrate. A similar adrenal-dependent increase in substrate was further found in 24-hour uninephrectomized rats and in rats with ceased urine excretion, while the increase after binephrectomy is non-adrenal-dependent and thus not due to ceased urine excretion.