To gain further understanding of the peptic complications encountered in renal transplant surgery, 84 patients (19 with chronic renal failure on dietary treatment, 29 on regular dialysis treatment, 36 with a well-functioning renal transplant) were studied with regard to gastric acid secretion capacity and serum concentrations of gastrin and group I pepsinogens (PG I). The mean duration of preoperative dialysis treatment of the dialysed patients was 13.7 months. The mean length of postoperative follow-up of the transplant patients was 10.1 months. There was no significant difference between the mean gastric acid secretion of the three groups of patients. All the means were within the reported reference interval for healthy controls. However, 26% of the non-dialysed, 17% of the dialysed and 28% of the transplant patients had gastric hyposecretion. The mean serum concentration of gastrin was elevated in all patient groups and unaffected by normalization of renal function through transplantation, unlike PG I, which was normalized by the procedure. Thus, in the present era of treatment of chronic renal failure with a relatively short period of dialysis treatment, the frequent gastric hypoacidity, which is known to be peculiar to non-dialysed uraemic patients, seems also to characterize dialysis and transplant patients.