It is intended to provide a novel oligopeptide which can be relatively easily produced, has not only a hair growth-stimulating effect but also an effect of promoting the growth of epithelial cells (for example, skin regeneration) and can easily pass through the horny layer to thereby reach the desired target cells in which its effects are to be exerted. Namely, water-soluble oligopeptides containing a proryl isoleucyl glycyl unit or an isoleucyl glycyl serine unit and having from 3 to 7 amino acids and water-soluble salts thereof.
