Two glycolipid fractions, isolated in 1975 from blood group A1 erythrocytes and shown on the basis of direct-inlet mass spectrometry to contain eight- and nine-sugar A-type sequences, have been reinvestigated by fast-atom-bombardment mass spectrometry and overlay analysis with selected monoclonal anti-A antibodies. The presence of three separate glycolipids was concluded, consistent with a common paragloboside backbone [beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-D-Glc] and a typical erythrocyte ceramide component (sphingosine, and 22-, 23-, 24-, and 25-carbon nonhydroxy fatty acids). It is proposed that they carry A determinants based on Type 1 [beta-D-Galp-(1----3)-beta-D-GlcpNAc], Type 2 [beta-D-Galp-(1----4)-beta-D-GlcpNAc], and Type 3 [beta-D-Galp-(1----3)-alpha-D-GalpNAc] chains, respectively. The Type 1 (eight sugars) and Type 3 (nine sugars) glycolipids appeared in mixtures of both the native and the acetylated form. The existence of Type 1 glycolipid, which appears to be a genuine erythrocyte glycolipid as concluded from the ceramide composition, had been predicted earlier by other workers.