Abstract: A disposable multi-cuvette rotor for use in an analytical photometer which comprises two injection molded parts from a transparent material of suitable chemical and absorption characteristics. These parts are joined together by ultrasonic welding and when so joined, define a plurality of radially-arranged cuvettes being separated by triangularly-shaped open spaces. Each of the cuvettes is divided into adjoining sample and reagent/measuring chambers by a wedge-shaped dam in a manner that the chambers are communicating with one another through an open space above the dam. There are pairs of recessed optical windows formed in both of the parts which are axially aligned and positioned adjacent the chambers of the greater radial distance so as to provide opposing planar walls defining an optical path through the chambers. There is provided a further integral optical window in the radial outer wall of each reagent/measuring chamber for use of the chamber in a light scattering or fluorescent measuring mode.