Peripheral blood mononuclear cells, obtained from patients with renal cell cancer and cultured ex vivo, exhibit high natural killer (NK) and lymphokine-activated killer (LAK) activity (also against allogeneic fresh tumour cells), which is transcribed into the hosts' immune status after reinfusion. Phenotypic analysis shows a slight increase in the percentage of CD56+ and CD8+ lymphocytes, while CD4+ lymphocytes decrease slightly. As a sign of activation an increase of cells expressing DR and CD25 antigens is observed. At the peripheral blood level, mononuclear cells show an increase, compared to basal values, of NK and LAK activity, especially at the end of the first infusion cycle. Phenotypic analysis of the patients' PBMC shows a decrease of CD3+CD4+ T lymphocytes and an increase of NK cells (CD3-CD56+CD16+) and of cells expressing activation markers (DR and CD25), particularly evident by the end of the second infusion cycle. Finally, in addition to the changes induced by IL-2 alone, reinfusion of incubated cells results in an activation of CD56+ and LeuM3+ cells.