The response of the human gynecological carcinoma cell-lines HEC-1-A (endometrial carcinoma) and OvCar-3 (ovarian carcinoma) to photodynamic therapy in vitro was examined. The porphyrin compound Photosan III (Ph III) was used for photosensitization of the cells after incubation times of 24 h (HEC-1-A) and 48 h (HEC-1-A and OvCar-3). The Ph III doses varied from 0-10 micrograms/ml medium. Irradiation was performed with laser light at 630 nm. Irradiation doses up to 20 J/cm2 were applied at an irradiance of 40-100 mW/cm2. Cell vitality of the untreated control groups and of the therapy group was determined 48 h after irradiation, using the trypan blue exclusion test. The experimental results show that treatment of OvCar-3 cells with 10 J/cm2 resulted in a decrease in vitality dependent on photosensitizer dose (0-5 micrograms/ml, 48 h incubation time) but independent of the irradiance (40-100 mW/cm2). Complete cell death was observed after application of irradiation doses in the range of 5-20 J/cm2 combined with drug concentrations of 10-2.5 micrograms/ml, at a fixed incubation time of 48 h. HEC-1-A cells did not survive photodynamic therapy with 10 J/cm2 after incubation with 5 micrograms/ml for 48 h. After a shorter incubation time of 24 h, 10 micrograms/ml Ph III was necessary for the same effect. There was a maximum decrease in cell vitality when measured 48 h after irradiation. This was not improved at 72 h.