OBJECTIVE: To determine the genetic relatedness of methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from six provincial hospitals in Hungary between 1993 and 1994. METHODS: Molecular fingerprinting methods were used: hybridization with a mecA-specific DNA probe after ClaI restriction; hybridization with a probe for Tn554; and pulsed-field gel electrophoresis after Smal digestion of chromosomal DNA. RESULTS: All strains were resistant to penicillin, oxacillin, erythromycin, gentamicin, tetracycline, imipenem, and cephalosporins, and variably resistant to ofloxacin, clindamycin and tobramycin; all isolates were susceptible to vancomycin. Forty-eight of the 51 isolates carried the mecA gene as determined by Southern hybridization, using a mecA-specific DNA probe, indicating that the methodology used for initial identification may have been in error in three of the cases. Forty-seven of the 48 mecA-positive isolates showed very similar genetic backgrounds as defined by pulsed-field gel electrophoresis (PFGE) patterns after Smal digestion of chromosomal DNAs: a unique PFGE pattern was seen in 32 isolates and minor variants of it in 15 additional isolates. All the 47 isolates carried the same mecA polymorph (Clal type III), as determined by DNA hybridization after Clal digestion of chromosomal DNA. Only one of the MRSA isolates had a completely different PFGE pattern and a novel mecA polymorph. CONCLUSIONS: The findings demonstrate the existence of a unique, epidemic MRSA clone, in both invasive and colonizing strains, which is widely dispersed in Hungarian hospitals hundreds of kilometers apart.