Temperature-sensitive labels are adhesive tags that display color changes at preset temperatures. There have been no studies of the suitability of this technology for measuring the temperature of blood components during transportation and storage. We used a digital thermometer to measure temperature in different locations inside containers of RBC as they were allowed to warm to ambient temperatures following removal from refrigeration. We compared these temperature readings with those of 3 temperature-sensitive labels. These labels are marketed to alert transfusion services if the temperature of blood bags exceeds 10 degrees C, which is the maximum permissible by Food and Drug Administration and American Association of Blood Banks requirements for transporting RBCs. The contents of refrigerated RBC units changed from one homogeneous temperature to a range of temperatures when containers were allowed to warm (undisturbed) to ambient temperatures. Color changes of all 3 temperature-sensitive labels correlated more with core compared with surface temperatures of RBCs units. These devices add an additional dimension of safety to the conventional 30-minute rule, which limits storage of blood components at ambient temperature to 30 minutes.