The time course of DNA polymerization, catalyzed by DNA polymerase I, can be monitored by following changes in light scattering that result from increases in molecular weight of the polymer. Increases in mass of 10% result in an easily measurable change in light scattering. It has been shown that the light scattering change is correlated with the incorporation of radioactive nucleotide, as measured by the filter binding method. Continuous monitoring of the time dependence of polymerization should prove useful in kinetic analysis of the polymerase reaction and related enzyme-DNA interactions.