After demonstrating through animal models that progenitor cells with haemopoietic regenerative capability are present in peripheral blood, such precursor cells were also found in the mononucleated cell (MNC) fraction of human peripheral blood. It was shown that such cells increase in the recuperative period following chemotherapy. A number of studies have demonstrated that autologous infusion of such MNC achieved by cytapheresis may lead to a quick restoration of haemopoiesis. The initial results of peripheral blood MNC achievement in 18 patients with different malignancies of the blood are presented in this paper. Ninety-one cytapheresis sessions were carried out, 88 with a Fenwall CS-3000 continuous-flow machine, and the remaining three with a Haemonetics V-50 discontinuous-flow cell separator. The number of sessions per patient ranged from three to six and the harvested MNC count was 19.3 x 10(9)/L, the percentage of recovery being 56.4%. Some studies are currently in course aimed to analyse the MNC subpopulations in order to measure the progenitor-cell fraction and to establish the viability of such cells for further transplants. Since only five patients have recently been transplanted, all successfully, no definite conclusions can be drawn presently in this connection.