Congenital dyserythropoietic anemia type II or hereditary erythroblastic polynuclearity with positive acidified serum test (HEMPAS) is a rare genetic disease inherited by a recessive mode. Previous studies on HEMPAS erythrocytes have shown that Band 3 and Band 4.5 glycoproteins were not glycosylated by lactosaminoglycans, while polylactosaminyl carbohydrates are accumulated as glycolipids (P. Scartezzini et al., Br J. Haematol., 51 (1982) 569; M.N. Fukuda et al., Br. J. Haematol., 56 (1984)55). Presently, we have isolated polylactosaminyl lipids from HEMPAS blood cells and analyzed their structures by fast atom bombardment-mass spectrometry (FAB-MS), methylation analysis, endo-beta-galactosidase digestion. The results indicate that polylactosaminyl lipids accumulated in HEMPAS erythrocytes are a species of poly-N-acetyllactosaminylceramides which are also present in normal erythrocytes, but at 7 approximately 9 times lower level. Isolated polylactosaminylceramides exhibit I-, i-, H- and Lex antigenic activities which suggest that the polylactosaminylceramides are derived from both erythrocytes and granulocytes.