Distribution of glyceroglucolipids in the mucous barrier of rat-stomach antrum, body and forestomach was investigated. Surface mucus lining and preformed intracellular mucus were obtained by perfusion in vivo of the ligated stomach compartments wit saline and 2 M NaCl. Lipids were extracted from dialyzed and lyophilized samples, and separated on DEAE-Sephadex into neutral and acidic fractions. The glyceroglucolipids contained in each fraction were quantified and then separated into individual components by thin-layer chromatography. Significant differences in the concentration of glyceroglucolipids in the separated areas of the stomach were found. The content of glyceroglucolipids in the antral portion of the stomach was five-times greater than that of the forestomach. The level of sulfated glyceroglucolipids was eight-times greater in the antrum as compared to the body and four-times greater as compared to the forestomach. One sulfated glyceroglucolipid was present in antral perfusates, whereas the body and forestomach contained two additional acidic glyceroglucolipids. Based on data of partial acid and alkaline methanolyses, oxidation with periodate and chromium trioxide, and methylation of the native and desulfated compound, the structure of antral glyceroglucolipid is proposed to be: SO3H(leads to 6)Glc(alpha 1 leads to 6)Glc-(alpha 1 leads to 6)Glc(alpha 1 leads to 6)Glc(alpha 1 leads to 3)-1(3)-O-alkyl-2-O-acylglycerol. The neutral glyceroglucolipid fractions from each area of the stomach were similar in composition and only variations in their concentration were observed. The data obtained suggest that the sulfated glyceroglucolipids are involved in the protection of the gastric mucosa of the antrum, since their concentration is greatest in this most acidic portion of the stomach which is also most often exposed to duodenal reflux.