The response of serum gastrin, insulin and glucagon to administration of sodium bicarbonate (SB) followed by cimetidine was studied in 35 duodenal ulcer patients. Relevant measurements were made using radioimmunoassay kits "Diagnostic" (USA) and "Oris" (France). It was established that SB administration induced a significant rise in gastrin levels while those of insulin, glucagon and gastrin lowered significantly following cimetidine treatment (gastrin levels progressed to baselines). This marked effect of cimetidine on the gut hormone production is not always due to its adverse action being rather of compensatory nature and directed at enhancement of cytoprotection and normalization of gastric secretion.