Microbiological investigations showed a positive culture in 430 out of 1540 venous catheters and shunts for dialysis. In 21 cases, a mixed culture with two different specific organisms was present. Of the total of 451 isolated organisms, 362 were gram-positive cocci and only 56 gram-negative bacillaceae. Staphylococcus epidermidis was by far the most frequent pathogen (n = 228), staphylococcus aureus in second place (n = 94). Among the gram-negative organisms, germs of the Klebsiella-Enterobacter group and Pseudomonas aeruginosa dominated. Staphylococcus aureus represented 31% of all germs isolated from Scribner shunts and Brescia fistulas. On the other hand the causative organism could be isolated in only 18% of the infected venous catheters. Staphylococcus aureus was the most frequent pathogen in septicemia due to catheters; in 16 out of 24 patients this microorganism was found in both cultures drawn from the blood and from the catheter. In 16 cases, a venous catheter led to septicemia, a shunt for chronical dialysis in 2 cases only. The frequency of infections caused by catheters can be significantly lowered by prudent care of the site of insertion, sterile handling and short indwelling time.