Staphylococcus epidermidis is the preeminent cause of nosocomial bacteraemia and infection of prosthetic medical devices. Bacterial adherence to biomaterial is a crucial early event in the pathogenesis of these infections. Antibiotics affect bacterial adherence to eukaryotic cells, capsule formation and biofilm production. However, results from studies involving coagulase-negative staphylococci are equivocal. In this study, the in-vitro adherence of radiolabelled bacteria was assayed to determine the effect of sublethal concentrations of a number of antibiotics on the attachment of four strains of S. epidermidis, with well-characterized adherence profiles, to intravascular catheters. The effect of antibiotics on biofilm production by S. epidermidis was assayed using a quantitative spectrophotometric assay. Although there was some strain-to-strain variability, none of the tested antibiotics affected bacterial attachment. However, treatment with cefazolin or vancomycin resulted in a significant decrease in biofilm elaboration. These data suggest that bacterial attachment by S. epidermidis, the initiating event associated with prosthetic device infection, cannot be prevented by subtherapeutic levels of fluoroquinolone, glycopeptide or beta-lactam antibiotics. However, later aggregative stages of adherence, associated with biofilm production, may be influenced by cell wall-active agents such as cefazolin and vancomycin.