Neutrophil attracting and activating factors that may already exist in normal cells are located.Polypeptides having neutrophil stimulating activity were isolated from an extract originating from a normal porcine heart, whereby the invention was completed. The invention provides (a) a polypeptide consisting of the amino acid sequence of SEQ ID NO:1; (b) a polypeptide consisting of an amino acid sequence derived from the amino acid sequence of SEQ ID NO:3 by deletion, substitution, insertion or addition of one or more amino acids and having neutrophil stimulating activity; or (c) a polypeptide consisting of an amino acid sequence biologically equivalent to the amino acid sequence of said polypeptide (a) or (b).