Five clusters of pseudobacteremias over a seven-month period were traced to a BACTEC® radiometric device. Four episodes were due to enterococcus and one involved Staphylococcus aureus. Each cluster began with multiple positive blood cultures from a patient with clinical evidence of bacteremia. On subsequent days each bottle in sequence yielded growth of the identical organism, as shown by phage typing and antibiograms. Cultures from patients believed to be infected with the organisms tested positive earlier (mean = 1.4 days) than those patients believed to be pseudobacteremic (mean = 4.8 days). Investigation pointed toward the BACTEC device as the most likely source. Resin beads were found in the needle on several occasions and were shown to be transferred from bottle to bottle. We postulated that contaminated resin beads or liquid from a positive bottle remained in the needle above the portion that was heat-sterilized, contaminating the next bottle when it was sampled.