Adherence ability to catheter materials for intravenous use of coagulase-negative staphylococci (CNS) which is frequently isolated from prosthetic implants and medical devices inserted into the body was studied, and the mechanism of catheter-associated infections and the prevention against that were discussed. Difference of the adherence ability of CNS to various kinds of catheter materials was found, and adherence ability to the catheter materials was correlated with that of human epithelial cells in culture. CNS isolated from intravenous catheters had higher adherence ability to the human epithelial cell cultures than isolates from other clinical sources. Among 4 kinds of catheter materials, including ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), silicone (Sil) and polyurethane (PUR), the adherence ability of CNS on the EVA containing barium was highest, and Sil treated with tungsten showed the lowest. The physicochemical properties of both the bacteria and the catheter materials, hydrophobicity of the bacterial cultures and the catheter materials, negative charges on surface of the bacteria, surface structure of the catheter materials, additives to the catheter materials, and coating the catheter surface gave great effects on the adherence of CNS to the catheter materials. In addition, as biofactors, fibronectin and PROTEAMIN-HICALIQ solutions enhanced the adherence of CNS. These results suggested that catheter materials having a smooth surface and higher hydrophobicity, treated with tungusten and coated with urokinase were effective on the suppression of the adherence to catheter materials. In addition to the improvement of catheter materials, aseptic procedures in catheterization were thought to be critical for the prevention of catheter-associated infections. In view of these results, it should be emphasized that coagulase-negative staphylococci is a major opportunistic pathogen in hospital-acquired infections.