Mitoses in normal and psoriatic epidermis.

The morning count of mitoses in uninvolved epidermis of psoriatics is not significantly different from normal skin. The afternoon count is higher than the morning in both, and significantly higher in uninvolved than in normal epidermis. These results may be interpreted as favouring the existence of a non-cycling G2 population in human epidermis. This G2 population could be released into mitosis by the factors involved in diurnal variation, and might be larger and more labile in psoriatics than in normals. The pathogenesis and aetiology of psoriasis may be related to such a G2 population.