[On the existence of a myeloproliferative factor in patients with a myeloproliferative syndrome (author's transl)].

Serum of patients suffering from a chronic myeloproliferative disorder (polycythaemia, era, osteomyelofibrosis, chronic myeloid leukaemia) and serum of lethally irradiated rats injected before application of a single doses of erythropoietin did not enhance the effect of erythropoietin -- measured with the iron incorporation rate of polycythemic mice. The rationale for these experiments is to try to find a "myeloproliferative factor", which augments the number of stem cells as described in sera of patients with polycythaemia vera, osteomyelofibrosis, and lethally irradiated mice.