The glyceroglucolipids content of basal and pentagastrin-stimulated gastric secretion was measured in male patients with gastric (12) and duodenal (12) ulcer. Six patients in each group received twice daily for a period of 4 weeks 150 mg of ranitidine, whereas the other patients received placebo. The glyceroglucolipids output in the basal secretion of patients with gastric and duodenal ulcer before treatment was similar and increased 2.7-fold after pentagastrin stimulation. In all patients treated with ranitidine, the mean output of glyceroglucolipids after pentagastrin stimulation increased from 1.38 to 2.05 mumol/h (P less than 0.05). This increase, however, was more pronounced in the duodenal ulcer group than in the gastric ulcer patients. No change in glyceroglucolipids output was noted in the patients treated with placebo. The ratio of glyceroglucolipids to HCl increased significantly (P less than 0.02) only in the ranitidine-treated patients.