A comparison was made between the percentage of T and B cells present in human blood on the day of collection and those recovered from whole blood specimens stored for one, two, and three days. In the peripheral blood of normal individuals, the percentage of E-rosetting and surface-membrane immunoglobulin-positive cells was unchanged throughout the three day period. Furthermore, whole blood samples from patients with various hematological diseases maintained for three days exhibited T- and B-cell percentages equivalent to those tested on day zero.