The presence of a Teflon catheter had no effect on the in-vitro activity of a range of antibacterial agents against slime producing and non-producing Staphylococcus epidermidis strains as determined by a microdilution assay. The susceptibility of S. epidermidis attached to Teflon catheters for 6, 24 and 48 h was also evaluated. MICs for planktonic and attached bacteria were similar. When bacteria attached to Teflon for 6 h were used as inocula, MBC values increased 32-8192-fold for the antibacterial agents tested. Similar results were observed when bacteria attached for 24 and 48 h were used as inocula. The activity of a high concentration (16 x MBC) of these antimicrobial agents against S. epidermidis biofilms in Teflon catheters was evaluated; for five slime non-producing strains, the highest reduction (around 99%) in bacterial viability was produced by cloxacillin and teicoplanin; for the slime producers, the highest effect (99.5% reduction) was shown by amikacin, clindamycin cloxacillin and ciprofloxacin but all cases still showed bacterial counts higher than 10(3) cfu/catheter segment. It is concluded that adherence of S. epidermidis to Teflon catheters decreases the bactericidal activity of the antibacterial agents tested in vitro.