Five novel diacylated sulfoglycolipids (1-5) were isolated from the cyanobacterium Scytonema sp. (TAU strain SL-30-1-4) and four novel acylated diglycolipids (6-9) were isolated from the cyanobacterium Oscillatoria raoi (TAU strain IL-76-1-2). These two groups of glycolipids and related known glycolipids isolated from these two and three other strains of cyanobacteria, Phormidium tenue (TAU strain IL-144-1), O. trichoides (TAU strain IL-104-3-2), and O. limnetica (TAU strain NG-4-1-2), were found to inhibit HIV-1 RT enzymatic activity to different extents. The structure elucidation of the various compounds is based on the selective hydrolysis of the glycerol ester moieties, GCMS analysis of the methyl ester derivatives of the liberated fatty acids, homo- and heteronuclear-2D-NMR techniques, and MS. The use of negative-ion FABMS for analyzing the combination and distribution of the fatty acids in glycolipids is demonstrated.