AbstractIt has recently become clear that cyclin‐dependent kinase (cdk) complex regulates the cell cycle by phosphorylating Rb protein, a tumor suppressor protein. It is likely that this complex is a target of various growth factors and anti‐growth factors (UV TGF‐β etc.) in keratinocyte (KC). It has also been suggested that abnormalities in the cell cycle regulating mechanism such as increased activity of cyclin‐cdk due to mutation of p53, a tumor suppressor gene, and overexpression of cyclin D may be concerned with carcinogenesis of KC. Thus, recent studies indicate that the cyclin‐cdk complex is a common target of proliferation and carcinogen