Elevated serum gastrin (SG) has been reported in chronic renal failure (CRF). We studied SG levels in relation to various humoral and gastroduodenal histopathologic findings in 20 controls, 12 uremics under conservative therapy (CT), 27 patients on regular dialysis (RDT) and 8 transplanted patients (Tx). SG and parathyroid hormone (PTH) levels were estimated by radioimmunoassay (RIA), in addition serum BUN, creatinine, Ca++PO4---and alkaline phosphatase (predialysis in RDT) were determined. 20 patients (12 on CT and 8 on RDT) underwent pentagastrin (PG) stimulation test and upper gastrointestinal endoscopy with biopsy of gastric and duodenal mucosa. The mucosal samples were stained for mucopolysaccharides (MPS), nucleic acid (NA) and alkaline phosphatase (AP), and divided into intense, normal or faint staining. Mean SG was 688.71 pg/ml (CT cases), 636.2 pg/ml (RDT cases) and 280.6 pg/ml (Tx cases), all values being significantly higher than controls (118.46 pg/ml). SG level had a linear correlation with serum creatinine in CT patients and predialysis creatinine in RDT patients, but not with other parameters studied (BUN, Ca++,PTH,PO4---AP). The incidence of gastroduodenal erosions (40%) had a significant negative correlation with SG. They were more frequent with normal MPS stain (p = 0.01) and NA staining (p less than 0.001) than faint staining of gastric mucosa biopsy. The acid response to PG stimulation was inversely correlated with SG. We believe that elevated SG is compensatory to a decreased response of the gastroduodenal mucosa to PG. Mere retention of SG does not explain its elevation as its correlation with serum creatinine existed not only in patients on CT, but also in RDT patients.(ABSTRACT TRUNCATED AT 250 WORDS)