Abstract: The object of this invention is a double multichromatic photometer including a single light-source and a single detector, particularly for the determination of chemical and clinical analyses, in which the photometer light comes from a single light-source which radiates along three distinct optical paths that converge onto a single detector; two of the optical paths are the first and the second measuring channels, which are alternatively excluded whereas the third optical path is for reference purposes. An optical collimation assembly and a measurement cuvette are inserted into each of the two measuring optical paths or channels. Within said three optical paths is inserted a rotating drum, said drum holds a number of interference filters, allowing the third reference optical path to pass freely, and inserts one filter at a time into one or the other of the two measuring optical paths.