On leukopheresis products obtained from patients included in a protocol interleukin-2/lymphokine-activated killer (IL-2/LAK) cell therapy, we analyzed, in parallel with the standard culture and on large volumes of these products, different parameters which could either improve LAK cell enhancement or simplify the procedure. We demonstrated first that purification of the mononuclear cells from the leukopheresis product before its culture is not required. An excess of red blood cells and granulocytes (up to 50%) in nonpurified samples improved both the mononuclear cell recovery in short-term culture (4 days) and the activation of LAK cells when the total nuclear cell concentration did not exceed 3 X 10(6)/ml. Different factors can contribute to this enhancing effect: the presence of red blood cells, the liberation of cytokines by granulocytes, or the loss of a population of activated lymphocytes, with liberation of cytokines by granulocytes, or the loss of a population of activated lymphocytes, with larger size and density than resting lymphocytes, during the separation. Supplementation of the medium with 2% heat-inactivated autologous plasma obtained before any treatment rather than with 2% pooled human AB serum does not modify the mononuclear cell recovery in 4-day culture, but it does enhance LAK activity. The inhibitory effect of heat-inactivated autologous plasma on proliferation and activation of LAK cells was never observed, suggesting the absence of suppressive factors in the plasma of the 23 analyzed patients. Similarly, autologous plasma did not modify natural killer and LAK cell functions when added during the cytotoxic assay.(ABSTRACT TRUNCATED AT 250 WORDS)