The invention relates to a method for acquiring data in order to determine organ function, in particular the liver or kidney function, comprising one or more polymethine fluorescent dyes having a fluorescence emission maximum, measured in ethanol, of less than or equal to 820 nm, and to the use of dyes as markers for acquiring data in order to determine the organ function. The invention further relates to a kit for determining an organ function with a marker dye, and to a device for acquiring data in the method.
