An isolated human megakaryocyte-colony stimulating factor (hMeg-CSF protein) preferably purified to homogeneity from urine of aplastic anemia patients is disclosed. The novel hMeg-CSF protein is a basic protein having a pI equal to about 7.2-7.4 as determined by isoelectric focusing and a molecular weight of about 29.000-34.000 daltons as determined by SDS-PAGE when in a glycosylated and sialyated form. The novel hMeg-CSF protein has the ability to induce the formation megakaryocyte-colony forming units in a murine fibrin clot assay in vitro, and the further ability to regulate megakaryocytopoiesis and platelet production in vivo. The hMeg-CSF protein can be further characterized as a glycoprotein having biantennary carbohydrate structures, beta-galactose residues as terminal or penultimate sugars and sialic acid moieties. The hMeg-CSF protein is believed to have a specific activity of at least about 4.000 CFU-Meg colonies/mg protein in murine fibrin clot assay. Unique pharmaceuticals containing the hMeg-CSF protein for treating animals including humans and methods for isolating the novel hMeg-CSF protein at various levels of purity are also disclosed.
