In the organ culture of adult human skin, long-term preservation of cultured epidermis was obtained when the culture temperature was shifted from 37°C to 32°C. The epidermal cell kinetics were compared for both culture temperatures using the findings of mitotic rate, mitotic distribution and autoradiographic labelling index with tritiated-thymidine (3H-TdR). As a result, it appeared that a lowered culture temperature controlled the cell cycle in vitro to maintain long-term, active epidermal proliferation.