A rapid method for determining the molecular weight distribution of polymers has been the aim of polymer chemists for a long time. The method presented here requires less than two hours, including dissolution of the polymer. It is an extension of a photoelectric turbidimetric technique presented by Taylor and Tung in 1961. The equipment has been completely redesigned and presently consists of a copper block containing a turbidity cell, optical system and attendant electronic circuitry for measuring relative changes in turbidity of polymer solutions as a function of temperature. An X–Y recorder is used to plot turbidity versus temperature. A parameter determined from the plot is correlated with a measure of molecular weight distribution determined on known samples for each type polymer by another means. Based on this correlation unknown samples may be analyzed. The instrument is easy to operate and has shown excellent stability over a two year period. Polymers studied by this technique include ethylene-propylene copolymer (EPR), polypropylene, polyethylene, and butyl, however, the only results to be reported here are those on ethylene-propylene copolymer.