Clinical strains of Mycobacterium tuberculosis. M. terrae complex, M. gordonae. M. auium-intracellulae complex, and M. fortuitum from Korean patients were isolated and analyzed by comparing large restriction fragment (LRF) patterns produced by digestion of genomic DNA with infrequent-cutting endonucleases like Asnl and Xbal, and pulsed-field gel electrophoresis (PFGE). Three M. tuberculosis, two M. terrae complex, two M gordonae, two M auium-intracellulae complex, and two M. fortuitum strains were compared by using Asnl and Xbal, and this allowed easy visual separation of all epidemiologically unrelated strains. PFGE exhibits different DNA restriction patterns which are easy to compare. Genome size of the strains roughly ranged from 3020 to 3335 kb. The LRF patterns are useful for epidemiologic studies of tuberculosis with regard to drug resistance.