A system for the determination of quantifies relating to the circulatory system of a patient including a device for the non-invasive measurement of the qualitative variation over time of the local concentration of an indicator injected into the blood circulation system at a first position, the measurement taking place at a second position of the blood circulation system. An evaluating unit is provided, in which there is implemented an evaluating algorithm which transforms the qualitative variation into a quantitative variation over time of the local concentration of the indicator injected into the blood circulation system. For the purposes of the transformation, the condition is fulfilled that the cardiac output COdye calculable from the quantitative variation over time of the local concentration in accordance with a predetermined relationship is equal to an input value of the cardiac output COe, which has been determined by thermodilution measurement.