PDT in dermatology is of growing interest and there are efforts to develop new sensitizers for topical application. Penetration potency of 9-acetoxy-2,7,12,17-tetrakis-((beta) - methoxyethyl)-porphycene (ATMPn), a novel sensitizer for topical photodynamic therapy, was studied in perilesional normal human skin from 58 melanoma patients and basal cell carcinomas of 12 patients. Single specimens of freshly excised perilesional skin (n equals 368) and basal cell carcinomas (n equals 28) were evaluated after topical application of an ATMPn solution for different time intervals (2, 6, 16 h) and subsequent preparation of cryostate sections (10 micrometer). Fluorescence distribution in tissue sections was estimated qualitatively using a score system respecting the morphological structure of human skin. In all examined sections of perilesional skin red fluorescence indicative of ATMPn was seen down to the basal layer of the epidermis using epifluorescence microscopy and optical multichannel analysis. Longer incubation times (16 - 20 h) revealed significant higher score sums as compared to incubation times of 2 or 6 h. However, basal cell carcinomas did not show time dependent differences in penetration. After 6 h penetration of ATMPn into the tumor, cell nests in the deep dermis were detected. These results indicate that there might be a faster penetration of this sensitizer in tumorous tissue as in normal tissue after topical application.