An optimized application of the photodynamic laser therapy for cancer treatment requires the knowledge of the effect of in-vitro parameters, such as biochemical targets and irradiation protocols, on the sensitizing efficiency. Sensitizers such as hematoporphyrin-derivatives react mainly via singlet oxygen formation with proteins and lipids within the cells when activated by light having the appropriate wave length. Singlet oxygen and oxygen radical formation can be determined by oxygen consumption of the reactants. An existing oxygen consumption measurement system was adapted for fast determination of the reactivity of the different parameters. Two examples of the applicability of the fast screening test system are presented here: Variation of the sensitizer to target ratio and the light intensity.