The influence of culture conditions on the differentiation of murine hemopoietic progenitor cesll was studied in semisolid culture.C57 BL/6(B6)bone marrow cells were seeded in plasma

agar and“serum-free”methylcellulose(SFM)culture containing impure and purified erythropoietin. After seven days

the culture were clotted

harvested

fixed and stained

and all colonies develop- ing on each plate were identified and scored in situ with respect to their lineage(s).The frequency distributions of the lineage classes under different culture conditions were then compared.The results showed that the expression of differentiation potentialities by hemopoietic progenitor cells in semisolid culture is strongly influenced by the nature of the culture medium in which the prog- enitor cells develop into colonies.Thus in any investigation of effects of regulatory factors on bemopoietic progenitor cells

the nature of culture medium in which the cells are proliferating and differentiating must be taken into account.Differential counting of colonies in situ in stained

clotted cnlture is useful for the investigation of conditions regulating progenitor cell differentiation.