Five patients in a newborn intensive care- unit (NICU) developed primary bacteremia due to Klebsiella during a 12-day period, May 22 through June 2, 1979, after feeding for 24-96 hr with contaminated breast milk. All patients had been fed via nasoduodenal tube with milk obtained from a single donor. The donor milk collected via electric suction pump was positive by gram stain for gram-negative rods and by culture for Klebsiella pneumoniae. A culture of hand-expressed milk was negative for gram-negative rods. The breast-pump tubing and safety trap were grossly contaminated with K. pneumoniae. Institution of proper sterilization of the pump equipment controlled the outbreak. This outbreak is the first documentation of nosocomial bacteremia as a major infectious complication of feedings of premature infants with contaminated breast milk.