A thyme extract, the preparation of which is described, produced a considerable stimulation of leucopoiesis and also an elevation of the thrombocyte count in the blood. In a comparative trial, the immunopotentiator 2-cyanoethylurea (BA1-4) has been found to be even more effective. The elevation of the leucocyte count is of importance not only to the various possibilities of immunostimulation, but also directly, in connexion with an elevation of the thrombocyte count, to the tumour-damaging process in the cancer multistage therapy, due to the promotion of the selective haemostasis set up on this occasion in the tumour tissue. The activation of immunological processes by intensive variants of the oxygen multistage therapy (O2-MT) increases in particular the efficiency of immunopotentiators so the latter should be used, in connexion with O2-MT, in any cancer therapy.