Seventy-four subclavian hemodialysis catheters inserted into 53 patients were studied prospectively. Sixteen of 64 assessable catheterization periods were complicated by clinically documented catheter-related sepsis, and 13 had an associated bacteremia. One patient died from catheter-related sepsis, and in two others, sepsis contributed to death. Staphylococci accounted for 11 bacteremias. Semiquantitative culture of the catheters indicated that 28 were significantly colonized. Comparison of these isolates with skin cultures from the insertion site suggested that the origin of the colonizing organisms was the skin (10 cases), intralumenal contamination (16 cases), or both routes (2 cases). Comparison of cultures taken during catheter insertion with those at removal rarely suggested that organisms introduced at insertion caused subsequent colonization. This study has demonstrated that infectious complications from using subclavian hemodialysis catheters exceed reported rates for all other modes of vascular access used for hemodialysis, as well as other indications for central venous catheterization.