The present study aims to find a method to reduce Staphylococcus epidermidis adhesion to acrylic and silicone--two materials used commonly in medical devices--by heparin and gentian violet surface preconditioning. Different periods of heparin preconditioning are studied to evaluate the influence of preincubation time on the reduction of bacterial adhesion. A two-hour period was chosen and applied in the adhesion assays with either heparin or gentian violet. Squares of the materials with adherent cells were also analysed by scanning electron microscopy (SEM). Results of adhesion assays showed a significant reduction (53-90%, P<0.05) in bacterial adhesion to silicone and acrylic after precontact with the conditioning substances. No statistical differences (P>0.05) were found between the extent of adhesion on silicone coupons precontacted either with heparin or gentian violet for each of the strains tested. On acrylic, heparin was more efficient (P<0.001) in reducing S. epidermidis IE186 adhesion than was gentian violet (85% and 53% reductions, respectively). Therefore, immersion of acrylic and silicone in heparin or gentian violet may constitute a simple and effective method by which to reduce S. epidermidis adhesion to medical devices.