A collaborative study involving 20 clinical laboratories representing diverse geographical regions was organized to examine the microbiology of evacuated blooc collection tubes. Overall, 14% of the 1433 tubes examined contained microorganisms representing a variety of bacteria and fungi. Of note was the finding that nearly 9% of tubes with yellow closures, which are stated to be sterile by the manufacturers, contained bacteria, including Pseudomonas aeruginosa, enterococci, Serratia marcescens, and Acinetobacter calcoaceticus. Sterilization of these potential sources of infection is advisable.