<p>A thrombocytotic factor comprising a physiologically active substance having the following amino acid sequence in its molecule: Xaa Gly Asn Asp Glu Ser Asn Ile Ser Phe Lys Glu Lys Asp Ile (wherein Xaa represents a non-specified amino acid residue) and having the activities of acting on the megakaryocyte-platelet system and thus accelerating the differentiation and maturation of megakaryocyte cells and the formation of platelets; and a medicinal composition for treating thrombocytopenia containing the above factor as the active ingredient. This substance is useful as the active ingredient of remedies and preventives for thrombocytopenia and thrombocytopenic purpura both accompanying chemotherapy and marrow graft and various diseases having a bleeding tendency caused supposedly by thrombocytopenia.</p>
