BACKGROUND Biochemical studies of organ blood group antigen expression show a mixed pattern originating from both the organ tissue and remaining blood cells trapped in the organ despite in vitro perfusion of the vascular tree. The blood group A glycolipid expression was studied in a unique case in which a human liver had been in situ perfused by recipient blood. METHODS A blood group O recipient was re-transplanted with an ABO incompatible A1Le (a - b +) liver. Because of discrepancy in size, liver segments II and III were removed 2 h after re-vascularization. Thereafter, the removed A1 liver segment was physiologically in situ perfused with O blood, eliminating a major part of the donor blood cells/plasma. METHODS Total neutral glycolipids were isolated from the liver tissue and separated by high-performance liquid chromatography. Purified glycolipid fractions were stained with anti-A monoclonal antibodies (mAbs) and structurally characterized by mass spectrometry and proton nuclear magnetic resonance (NMR) spectroscopy. RESULTS Two blood group A reactive glycolipid compounds were isolated. One component had a thin-layer chromatography (TLC) mobility as a six-sugar glycolipid and reacted with mAbs specific for A type 1 mono-fucosyl structures. The second glycolipid fraction migrated as seven-sugar components and reacted with mAbs specific for type 1 difucosyl (ALeb) as well as Leb determinants. Mass spectrometry of the six-sugar component showed a structure similar to a blood group A hexaglycosylceramide with one fucose. Mass spectrometry and proton NMR spectroscopy of the seven-sugar fraction revealed a mixture of blood group Leb hexa- and ALeb hepta-glycosylceramides, respectively. All fractions were non-reactive with antibodies specific for A antigens based on types 3 and 4 core chain structures. In addition, TLC immunostaining of glycolipids isolated from blood group A livers, harvested for organ transplantation but discarded for various reasons, revealed trace amounts of several A glycolipids with a complex pattern. CONCLUSIONS The in situ perfused liver tissue contains blood group A glycolipids based exclusively on type 1 core chains. The secretor gene (Se) codes for a fucosyltransferase acting on all core chain precursors while the H-gene fucosyltransferase only utilizes the type 2 chain precursor. Whether this explains that only A type 1 chain compounds were found has to be established.