A dose-response gastric secretion test was performed in 87 nondialyzed patients with chronic renal failure (CRF) and in 87 age- and sex-matched controls without renal disease. Twenty-six of the CRF patients were reexamined, 18 undergoing regular hemodialysis and 8 after successful transplantation. The gastric acidity, acid output, and volume output of the nondialyzed CRF subjects were decreased when compared with those of the controls or of patients in the posttransplant phase. This decrease was more marked with low than with high stimulant doses. The decrease in acid output was significantly greater than that in volume output. Moreover, when compared with the dialysis phase the nondialyzed patients had lowered gastric acidity and acid output, but no decrease in volume output was evident. The results indicate that there is an inhibition of gastric secretion in CRF. This inhibition is dependent on strength of stimulation and is abolished by active treatment of CRF, more clearly by transplantation than by maintenance dialysis. In addition, the inhibition is predominantly on the secretion of acid, the output of gastric juice being less affected.