method for determining and selecting effective or non-effective therapeutic drug combinations for patients by means of individual in vitro tests on living patient samples before or during therapy, characterized in that the efficacy measurement is performed on living cells, wherein living cells consist either of fresh tumor tissue samples or tissue samples from other diseases or healthy tissues or blood samples or cells obtained from tissue or blood and cultured outside the body, and thereby continue to possess as far as possible the original properties of the cells from the body. However, the cells may also be comparably treated according to the treatment of the patient outside the body. characterized in that for the efficacy measurement the individual drugs are measured in their most optimal concentration and their combination efficacy is combined by calculation, wherein the statement of inefficacy or efficacy is determined with the aid of the theoretical distribution curve and the optimum concentration of a single drug is characterized in that the PCIs (Percent Cell Growth Inhibition) or data of other efficacy readouts of differently tested living cells give a PCI range or data range of other efficacy readouts as wide as possible and the theoretical distribution curve results from the mathematical combination of the distribution curves of all individual substances involved in the combination. characterized in that the arithmetical combination of the efficacies of the individual substances is determined by summing their PCIs (Percent Cell Growth Inhibition) or data of other efficacy readout methods and dividing by the number of substances of the combination, wherein the theoretical distribution curve is characterized by calculating the mean values for the averages, medians and standard deviations of the distribution curves for the individual substances. characterized in that the efficacy measurement is performed on living cells, wherein living cells consist either of fresh tumor tissue samples or tissue samples from other diseases or healthy tissues or blood samples or cells obtained from tissue or blood and cultured outside the body, and thereby continue to possess as far as possible the original properties of the cells from the body. However, the cells may also be comparably treated according to the treatment of the patient outside the body. characterized in that for the efficacy measurement the individual drugs are measured in their most optimal concentration and their combination efficacy is combined by calculation, wherein the statement of inefficacy or efficacy is determined with the aid of the theoretical distribution curve and the optimum concentration of a single drug is characterized in that the PCIs (Percent Cell Growth Inhibition) or data of other efficacy readouts of differently tested living cells give a PCI range or data range of other efficacy readouts as wide as possible and the theoretical distribution curve results from the mathematical combination of the distribution curves of all individual substances involved in the combination. characterized in that the arithmetical combination of the efficacies of the individual substances is determined by summing their PCIs (Percent Cell Growth Inhibition) or data of other efficacy readout methods and dividing by the number of substances of the combination, wherein the theoretical distribution curve is characterized by calculating the mean values for the averages, medians and standard deviations of the distribution curves for the individual substances.