The pteridine neopterin (NP) was shown to be produced by monocytes and has been known as a userul maker of immunological activation, although, the biological activity of this agent is still unclear. To <.'!ucidate the biological function of NP, the changes in the number of blood leukocyte, bone marrow ,md spleen hemopoietic progenitor cells after intraperitoneal administration of NP into mice were in-\· cstigated. Administration of NP increased the number of blood leukocytes about 2 fold higher

more »

... than that of the control at days 7 and 14. Blood films, made by smearing samples of peripheral blood, showed the increment of granulocytes in blood of NP treated animals. The number of granulocyte-ma--:rophage progenitor cells (CFU-GM) was also increased in both bone marrow and spleen in mice with ~p administration . Extensive study showed that NP stimulated the hematological recovery in bone marrow transplanted animals . All these findings suggest that NP has a stimulating activity on hemopoiesis by afiecting the proliferation and differentiation of hemopoietic progenitor cells in vivo.