Most transfusion services discard unopened units of blood that have been returned to the blood bank more than 30 minutes after the issuance or have attained a temperature of more than 10 degrees C. The objective of this study was to learn the prevalence of bacterial growth, if any, in the units of blood that were exposed twice, for six hours each time, to room temperature during their refrigerated storage. All of the 396 units cultured were negative except one red cell unit that grew a Bacillus species, probably B. subtilis. Further studies suggested that the growth of B. subtilis was due to laboratory contamination. The authors concluded that more work is needed to study the bacterial growth and the effect on red cell enzymes in the units of blood that are exposed to room temperature for varying periods or are returned to the blood bank after 30 minutes of issuance. If no adverse effect is noted, the policy of not reissuing such units may need revision so that more units could be salvaged.