PUVA-therapy (P=psoralen, UVA=UV-radiation), a particular type of chemotherapy for proliferative cutaneous diseases (psoriasis, mycosis fungoides and others) and pigmentation disorders (vitiligo) is realized by oral or topical administration of a linear furocoumarin-psoralen and successive irradiation of the skin with UV-A light. Antiproliferative activity of psoralen derivatives is due to monofunctional and bifunctional lesions in the cell DNA (formation of mono-adducts and di-adducts). To these latter lesions (interstrand crosslinkages between the two polynucleotydic chains of DNA) are mainly ascribed some undesired side effects of PUVA-therapy (phototoxicity, erythema, skin cancer). The drugs used in PUVA-therapy are methoxsalen (8-MOP), bergapten (5-MOP) and trioxsalen (TMP). Although the photochemotherapy by means of psoralens is presently the most effective treatment of psoriasis and similar deseases.