An outbreak of candidemia involving five infants receiving total parenteral nutrition in the neonatal intensive care unit was investigated. Cultures of the intravenous fluids demonstrated that the retrograde medication syringe fluids were significantly more likely to be contaminated with Candida than were other fluids being administered to the infants (p less than 0.001). Candidemia was significantly associated with total parenteral nutrition (p = 0.04) and retrograde medication administration (p = 0.02). A survey of nursing practice found that reuse of the retrograde syringes was the most likely cause of contamination. Molecular typing showed that the strains of Candida albicans that were isolated from the bloodstream were also found in the retrograde syringes and that at least three strains of C. albicans and one strain each of Candida tropicalis and Candida parapsilosis were involved. In vitro growth curves demonstrated that Candida species had a selective growth advantage versus bacteria in the total parenteral nutrition fluid. An in vitro simulation of the retrograde medication administration system suggested that the outbreak probably developed after the frequency of changing intravenous tubing was decreased from every 24 hours to every 72 hours. The outbreak was terminated by using syringes only once and resuming intravenous tubing changes every 24 hours. Retrograde medication administration in association with total parenteral nutrition may increase the risk of Candida line infection.