One hundred and thirty-eight strains of Mycobacterium tuberculosis isolated from the 7th nationwide tuberculosis prevalence survey in 1995 were subjected to the restriction fragment length polymorphism (RFLP) analysis using IS6110 probe to define the representative fingerprinting patterns of Korean strains of M. tuberculosis and to evaluate the usefulness of DNA fingerprinting in tracing the transmission link of M. tuberculosis. Among 138 strains, 129 different IS6l10 RFLP types were identified. The number of bands in IS6110 RFLP types diversed from 1 to 20, and the majority (75%) was 9 to 14 bands. The RFLP patterns of 8 out of 15 strains isolated from the follow-up survey of one and half year later after the 7th national TB prevalence survey were unchanged when compared with previous RFLP patterns. Fifteen (11%) out of 138 strains were grouped in 6 IS6110 clusters; 2 with 10 copies, 2 with 12 copies, 1 with 14 copies, and 1 with 17 copies. These clusters were unable to be subclassified by IS1081 or (GTG) probes except one cluster by pTBN12 probe. The transmission links of 2 clusters were deducible; one from household and another from neighborhood, but those of remaining clusters were unclear because they had no contact one another. The results suggest that vigorous transmissions in tuberculosis are still progressing in Korea.