Use of a polypeptide derivative that has a receptor binding activity of the growth hormone secretagogue and, thus, raises the concentration of intracellular calcium ion, or a salt thereof, to prepare a medicament to promote liver regeneration, recover liver function or promote recovery after hepatectomy, in which the polypeptide derivative is (i) a polypeptide derivative in which, in an amino acid polypeptide sequence, which has an amino acid sequence selected from the group consisting of amino acid sequences represented by SEQ ID Nos: 1 to 22 and an amino acid sequence in which one to five amino acids are deleted, substituted or added in a position other than the first to fourth amino acid residue in said amino acid sequences, the second or third amino acid residue from the amino terminal end has a group represented {in which R1 and R2 are the same or different, and represent -T1-P1-Q1 (in which T1 represents a divalent hydrocarbon group of 1 to 20 carbon atoms, P1 represents -CO-, -SO2-, -CO-O-, -O -CO-, -O-, -CO-S-, -S-CO-, -CS-S-, -S-CS-, -S-, -CO-NR4-, -NR4-CO-, -CO -NR4-CO-, -CS-NR4-CS-, -SS-, -CS-NR4- or -NR4-CS- (R4 represents a hydrogen atom or a C1-4 alkyl group), and Q1 represents an atom of hydrogen, an optionally substituted C1-35 alkyl group, an optionally substituted C2-35 alkenyl group, an optionally substituted C3-8 cycloalkyl group, an optionally substituted C1-6 alkyl-C3-8 cycloalkyl group, a C6-14 aryl group optionally substituted or an optionally substituted C7-16 aralkyl group), -P1-Q1 (in which P1 and Q1 are the same as defined above) or -Q1 (in which Q1 is the same as defined above), with the condition that when one of R1 and R2 is Q1, the other represents -T1-P1-Q1 (in which T1, P1 and Q1 are the same as defined above) , or -P1-Q1 (where P1 and Q1 are the same as defined above)}； (ii) a polypeptide derivative having an amino acid sequence from the first to the tenth amino acid from the amino terminal end in the amino acid sequences represent
