Interleukin-4 (IL-4) is a pleiotropic immunomodulatory cytokine produced mainly by T lymphocyte. It is known that many kinds of non-haematopoietic cells, as well as immune cells and haematopoietic cells, express IL-4 receptors. Recently, we found that IL-4 increased hydroxyproline and osteocalcin accumulation and caused mineralization in cultured human osteoblast-like cells. To clarify the mechanism of those effects of IL-4, we explored mRNAs whose expression levels were increased or decreased by IL-4 treatment using the method of differential display. As a result, expression of pro-alpha 1(VI) collagen gene in osteoblast-like cells proved to be substantially enhanced by IL-4 treatment. Considering that type VI collagen binds many kinds of extracellular matrices, type VI collagen probably mediates IL-4-dependent increase of accumulation of hydroxyproline and osteocalcin in cell layers of osteoblast-like cells.