The needs for laboratory size reaction injection molding (RIM) equipment are reviewed. Three application areas are identified: Process development, chemi cal system development and chemical system research with interface to analyt ical instruments. The size of the machine, its flexibility and quantity of reac tants required for each of these areas is reviewed. Commercially available machines, those described in the literature, and several built at the University of Minnesota are compared. Polyurethane RIM properties from lab scale machines show good agreement with production parts. Our “micro RIM” machine for chemical system research is described in detail. Equations for pressure drop and viscous heating are given.