We investigated the usefulness of the restriction enzyme (RE) fingerprinting for epidemiological tracing in gonococcal disease. The RE patterns of three paired gonococcal isolates showed corresponding identical fingerprints. Within each of the three pairs of epidemiologically linked isolates the respective restriction patterns were completely identical. Also, the restriction patterns of 6 strains from a larger contact group were identical. Identical restriction patterns were also obtained in each of the two cases where isolates were recovered from both urethra and cervix. The serological findings were in perfect agreement with the genomic fingerprinting as to the identity between all strains of the same epidemiologic chain. Relapse of the original infection could be excluded in one case by the finding of a different RE pattern and also a different serovar pattern of the strain recovered 4 months later.