The Mycobacterium chelonae-like organism (MCLO) is a recently described member of the Mycobacterium fortuitum complex which causes posttraumatic skin infections and catheter sepsis. This taxon is a distinct group biochemically and has a unique mycolic acid profile as determined by high-performance liquid chromatography. Its phylogenetic relationships to other mycobacteria, however, have not been studied previously. We sequenced 1,062 bp of the 16S rRNA genes from three MCLO strains obtained from the American Type Culture Collection and compared our results with the sequences of previously described taxa of rapidly growing and slowly growing mycobacteria. Two biochemically typical strains (ATCC 49650T [T = type strain] and ATCC 49651) had identical sequences, while the sequence of a biochemically atypical strain (ATCC 49649) differed by 4 bp from the sequence of the two typical strains. The Hamming distances between these MCLO strains and related rapidly growing mycobacteria are comparable to the Hamming distances among taxa of rapidly growing mycobacteria established as species by DNA-DNA hybridization. We propose the name Mycobacterium mucogenicum sp. nov. for this new taxon because of the highly mucoid nature of most isolates on solid media.