Abstract: The viability of leukocytes or specific fractions of leukocytes is maintained by drawing blood from a donor or patient into a mixture of an anticlotting agent and a basic salt solution (BSS) or a minimum essential medium (MEM) which solution or medium sustains the viability of the leukocytes in the blood, then layering the blood-MEM or BSS mixture on a Ficoll-Hypaque solution and centrifuging to separate the leukocytes. The resulting leukocytes are diluted to about 0.5.times.10.sup.6 viable cells per ml. in BSS or MEM containing antibiotics and fetal calf serum or serum substitutes equivalent thereto. The resulting suspension is transferred into sterile containers at room temperature so that each container has about 2-10.times.10.sup.6 cells. The containers are then packed into insulated containers and are ready for shipping.