A reaction injection molding process is disclosed comprising:introducing a mixture of substantially stable reactant streams into a mold, said mixture, in the aggregate, containing polyamide polymer forming compounds and polyurethane polymer forming compounds, said polyamide polymer forming compounds including lactam, an anionic polymerization catalyst and a polymerization activator, said polyurethane polymer forming compounds including a polyol, a polyisocyanate, a chain extender if desired, and a polyurethane polymerization catalyst, said polyamide polymer forming compounds and said polyurethane forming compounds reacting to respectively form polyamide and polyurethane polymers in said mold to thereby yielding a reaction injection molded product composed of said polymers; andrecovering said product from said mold.