The mycolic acids were isolated from Mycobacterium gordonae (strain ATCC 14470), and purified by thin layer chromatography. Three species were studied by mass spectrometry. The analogy between M. gordonae and M. leprae, based on the lack of tuberculostearic acid, was supported by the comparison of the structures of their mycolic acids. Succinct analyses of the lipids of three other scotochromogenic strains of mycobacteria, using thin layer chromatography and gas-liquid chromatography, were performed. These strains were more remote from M. gordonae than is M. leprae, as far as the lipid content is concerned.