The determination of the T and B subpopulation percentages and lymphocyte blastogenic response functions are useful tools to evaluate and monitor disorders associated with immunodeficiencies, lymphoproliferations, malignancies, infections, inflammations, and autoimmune diseases. Comparative studies of cryopreserved lymphocytes frozen at - 190 degrees C over a period of one year obtained by lymphocytapheresis of normal donors and fresh lymphocytes found no significant changes of lymphocyte subpopulations or blastogenic response functions. These cryopreserved lymphocytes can therefore be used as a reproducible quality control reagent. Comparisons of the stability of T and B populations of fresh, one, two, three, four, and five day old culture medium (RPMI 1640) stored separated peripheral blood lymphocytes and culture medium (RPMI 1640) stored one, two, three, four, and five day old whole peripheral blood revealed that culture medium prolonged the viability to approximately three days. It seems feasible for smaller clinics and hospitals that lack the facilities to run tests on lymphocytes to mix their heparinized blood with culture medium and then transport it to laboratories where the tests can be performed.