Immunohistochemical localizations of 3',5'-cyclic AMP (cAMP) and 3',5'-cyclic GMP (cGMP) were performed in the involved and non-involved epidermis of psoriasis and in the normal controls. The following results were obtained: 1. In the normal epidermis, cAMP was located in the cytoplasm throughout the epidermis but it was more pronounced in its upper portions, especially in the granular layers. Occasionally it was also observed in the nuclear membrane. However, cGMP was located mainly in the cytoplasm of the lower layers of epidermis, though the fluorescence was less pronounced as compared with that of cAmP. 2. In the noninvolved psoriatic epidermis, the localization pattern of cAMP was basically similar to that in the normal control, but its fluorescence seemed more pronounced. The fluorescence of cGMP was essentially the same as that in the normal control. 3. In the involved psoriatic epidermis, the distribution pattern of cAMP was essentially the same as that in the normal control, but its fluorescence seemed more pronounced. Marked increase in the fluorescence of cGMP was observed in the involved psoriatic epidermis, though it was much more pronounced in its lower portions.