Two models describing the laminar flow of a polymerizing liquid through a tube have been developed and tested experimentally. One model is a full finite difference solution of the balance equations. The other is an approximate analytical solution which assumes that flow ceases after viscosity increases about tenfold. The models are compared to two experimental cases: (1) the pressure rise needed to keep the flow rate through the tube constant and (2) the flow rate decrease when pressure at the tube entrance is held constant. The finite difference model is more accurate in the early stages of polymerization while the approximate analytical model is more accurate at long times. The models have application to runner flow in reaction injection molding, to nozzles in thermoset molding, to thermoset dispensing equipment and to continuous reactive polymer processes in general.