Microbial contamination occurred in 23 (13 per cent) of 177 cadaver donor kidneys prior to renal transplantation. In 16 cases there were no complications directly attributable to the organisms recovered from the preservation media. Three patients developed perinephric infections associated with renal artery anastomotic disruption and required emergency transplant nephrectomy. A fourth patient developed renal artery stenosis and a hypogastric artery aneurysm that required correction 6 months later with preservation of renal allograft function. In 3 cases no follow-up information was available. None of the 154 uncontaminated kidneys developed arterial disruption or aneurysm. Candida albicans and Pseudomonas aeruginosa infections were responsible for the nearly disastrous arterial disruptions and possibly the hypogastric arterial aneurysm. These findings demonstrate the importance of bacteriological surveillance of perfusion media to detect nosocomial infection, to guide antibiotic chemotherapy and to direct surgical management of septic complications. In our experience contamination was not necessarily incompatible with long term satisfactory results; however, when complications did occur they were serious. It is likely that the size of the microbial inoculum, the patient's immune competence and the protective effect of antibiotic therapy administered to the donor and recipient affected the eventual outcome.