BACKGROUND: Toxic shock syndrome toxin 1 (TSST-1) is an important pathogenic factor in toxic shock syndrome, and its structural gene, tst has been cloned and sequenced, many of its biological and physicochemical properties have been determined, and immunostimulatory properties such as TNF production have been assigned to it. We investigated to know the proportion of strains possessing tst gene among pathogenic Strains of Staphylococcus aureus isolated from hospitalized patients and to elucidate the coexistence of mecA gene and tst gene. METHODS: S. aureus strains isolated in Asan Medical Center from December 1996 to June 1997 were incubated in brain-heart infusion media and harvested. Chromosomal DNA was prepared and polymerase chain reaction (PCR) was performed to detect mecA gene and tst gene in pathogenic S. aureus. RESULTS: A total of 126 strains were included. Among these, 11 strains (8.7%) were positive in PCR for tst gene. Ten out of these were mecA-positive strains and only one was mecA-negative. That is to say, among 60 strains of mecA-positive MRSA, 10 (16.7%) were tst-positive, and among 66 strains of mecA-negative MSSA, only one (1.5%) was tst-positive. CONCLUSION: Among S. aureus isolated from hospitalized patients, tst- possessing strains were 8.7%. TSST-1 gene was more prevalent in mecA-positive S. aureus than in mecA-negative S. aureus.