Slime formation was detected in Staphylococcus epidermidis strains isolated from either infected patients or healthy individuals. Cells of S. epidermidis, that either formed slime or not, adhered to teflon catheters. There was no correlation between adherence of bacteria to teflon catheters and slime formation. Clindamycin at subinhibitory concentration significantly inhibited slime formation without inhibiting bacterial growth. Adherence of S. epidermidis to teflon catheters was affected by the presence of clindamycin whether slime was produced or not. Clindamycin at subinhibitory concentrations markedly inhibited hemolysin production by S. epidermidis without appreciably altering the cell density, and cells grown in the presence of the drug showed very low hemolytic activity upon disruption. These results suggest that clindamycin at low concentration alters S. epidermidis virulence properties, apart from inhibiting growth.