Representative strains of M. senegalense and an unusual strain, labelled M. farcinogenes (M280) were examined by thin-layer chromatography for the presence of characteristic surface glycolipids. In the case of M. farcinogenes M280 and M. senegalense M264, the glycolipids were of the alkali-labile acyltrehalose lipooligosaccharide (LOS) class of antigens, whereas M. senegalense M263 was found to contain the alkali-stable glycopeptidolipids (GPL). Through a combination of 1H-NMR, methylation analysis, FAB/MS, and other analytical techniques, the structures of these glycolipids were deduced. The LOS glycolipids were found to be similar in structure to the characteristic glucosyltrehalose-based glycolipids isolated previously from clinical isolates of M. fortuitum, but distinct from the diacyltrehaloses characteristic of the type strain of M fortuitum. The glycopeptidolipids from M. senegalense M263 were closely similar to those characterized previously from M.