Prodigious quantities of blood are withdrawn from critically ill patients in intensive care units, adding to the cost of their care and, more important, to their morbidity. We undertook a simple study to record the volumes of blood drawn in two intensive care units. In one, specimens were ordered by the physicians, and in the other, blood was drawn in accordance with a protocol. Volumes of blood discarded to clear indwelling lines were also measured. After the staff had been informed of the results and the use of smaller collecting tubes had been instituted, a repeat study showed that the mean volume of blood drawn was reduced by nearly half. We suggest that only pertinent laboratory tests be ordered, that procedures to avoid discarding part of the sample be adopted, and that smaller collection tubes be used when appropriate.