Photodynamic therapy (PDT) with laser radiation opens a new field in the treatment of malignancies. We evaluated the phototoxic effects of five different substances for photodynamic therapy in concentrations showing no systemic toxicity. We used gynecologic tumor cells and evaluated the photodynamic effects for cell growth in a colony-forming assay. For Indigocarmin we found a reduction in the colony-forming assay compared to the control group from 87% to 66% after irradiation at 50 mumol/l and 608 nm wavelength. "IR 132" showed a reduction in the colony-forming assay from 73% to 72% 50 mumol/l (590 nm). For the incubation of the HeLa cells with 50 mumol/l of "Sulfo-Phthalocyanin" we found a reduction of the colony-forming potential from 81% to 67% (595 nm). The most strikingly differences were found for the incubation and irradiation of Methylene Blue, showing a reduction from 77% to 16% caused by a toxic effect of the substance itself (5 mumol/l, 660 nm) and "Sulfo-Aluminium-Phthalocyanin" stained cells, which shows a reduction from 86% to 17% (50 mumol/l, 675 nm). We see the possibility of a photoactivation and cell devitalisation by "Sulfo-Aluminium-Phthalocyanin" and laser radiation. A future clinical trial would seem justified.