Numerical analysis of 211 strains of rapidly growing, nonphotochromogenic mycobacteria was carried out by using 116 characters. New species reported after 1981 and not yet compared with known species by numerical classification were included. At the level of 90% of the matching coefficient, the following species could be differentiated from each other and were shown as distinct clusters: Mycobacterium pulveris, M. moriokaense, M. chitae, M. diernhoferi, M. porcinum, M. fortuitum, M. chelonae subspecies chelonae, M. chelonae subspecies abscessus, M. smegmatis, M. agri, M. fallax, M. parafortuitum, M. fortuitum subspecies acetamidolyticum. Four taxa, M. fortuitum, M. porcinum, M. chelonae subsp. chelonae, and M. chelonae subsp. abscessus, were regarded as distinct. However, these were combined into one large cluster at a level of 90% of the matching coefficient and, therefore, were regarded as forming one series or complex. M. fortuitum subsp. acetamidolyticum was reported as a subspecies of M. fortuitum, but this was differentiated clearly from the other species including M. fortuitum.