Molded plastic gears and transmissions must work effectively in extremely variable conditions just as their counterparts in steel. Plastics have the added variables of large thermal expansion and contraction@ moisture absorption@ greater tolerance variation@ lower strength@ and form deviations due to the molding process. The design of a molded transmission must consider these effects and characteristics. This paper will offer an example of the development of a molded plastic gear pump intended for the very steady delivery of 50 psi water pressure for a medical application. It will present our approach in design@ tolerancing@ material selection@ molding procedure@ and testing to achieve and verify an effective as-molded transmission.