By using the colcemid method, the presence of a diurnal variation for the mitosis index was confirmed, showing a definite minimum during the night in the sebaceous gland of the Syrian hamster ear. Furthermore, the number of all labelled cells and the quotient "single-labelled 14C-cells + double-labelled cells/single-labelled 3H-cells" determined with double-labelling autoradiography ([3H] and [14C]thymidine) seem to be subject to rhythmic fluctuations, although statistical support for this observation is lacking. The parallelism of the rhythmic variations in the epidermis and in the sebaceous glands is striking.