One of virulence factors produced by Staphylococcus aureus is staphylokinase (SAK), which enhances their proteolytic activity leading to tissue damage and improving bacterial invasiveness. In the present study we estimated the ability to produce staphylokinase by 95 S. aureus reference strains and clinical isolates from the airways of cystic fibrosis patients, from skin lesions and from infected bones. We would like to verify any relationship between SAK production and the types of clinical isolates as well as other biochemical properties and activities of these staphylococcal strains, which can be important for their pathogenicity. More than 62% of all tested strains were able to produce secreted type of SAK. Staphylokinase production was significantly more common in the isolates from skin and soft tissue infections than in any other group of tested staphylococci. The general tendencies in the selected properties or activities of both SAK(-) and SAK(+) isolates were similar. Our data confirm phenotypic dissimilarity in SAK production of S. aureus strains isolated from various types of infections. It is compatible with the biological role of staphylokinase and with hypothetical model of staphylokinase mediated bacterial invasion of host tissues. Thus, the estimation of SAK production by S. aureus isolates may be regarded as the parameter describing potential invasiveness of staphylococci and can be useful as a medical recommendation for the eradication of staphylococci carrier state.