The adherence of bacteria to pediatric IV catheters and needles was studied. Scanning electron micrographs showed that bacteria adhered well to the catheters and needles, mainly to non-smooth surface areas.In vitroquantitative determination, with the use of radiolabeled bacteria, revealed differences in the affinity of bacteria for the various IV cannula materials. The adherence per square area was greatest for plastic catheters, less for steel needles, and least for siliconized needles. Mean values for the adherence of Staphylococcus aureus to these cannulae were 37.9-40.3 x 105bacteria/cm2for the plastic catheters; 10.2 x 105bacteria/cm2for the steel needles, and 7.2-7.6 x 105/cm2for the siliconized needles. Removal of the glutaraldehyde-fixed bacteria adhered to the cannulae, after their placement in veins of rabbits, was lower for the plastic catheters than the IV needles. The appearance and severity of venous phlebitis produced by the various cannulae was determined in an animal model. The degree of the inflammatory response elicited correlated with thein vitrobacterial adherence, indicating that bacterial adherence plays a role in the appearance of cannulaassociated phlebitis.In view of our results and other previous observations of lower rate of infections with the use of IV needles, it is suggested that needles should be preferred to plastic catheters whenever possible. The describedin vitroassay for bacterial adherence can be used to determine the adherent properties of IV cannulae, which should be considered in any future cannula design.