Photochemotherapy with psoralens today represents an integrated method in the therapeutic spectrum of several dermatoses. At present, mainly 8-methoxypsoralen is applied as photosensitizing agent. Against a background of a clinically observed lower rate of acute side effects of 5-methoxypsoralen-PUVA phototoxic reactions of these two photosensitizers were investigated by estimation of the erythemal response on human skin and quantified by measuring the mouse ear edema. In addition, cytotoxic effects were demonstrated by the Candida test. Two types of UVA-fluorescent tubes with UVB-emission ranging form 1 to 9 per cent were used. Results are discussed in respect to their clinical implications and the action spectra supposed for the two photosensitizers.