The polymerization of unsaturated monomers can be initiated by ultraviolet radiation. This method of initiation has been used to form polymers, to graft polymerize monomers onto existing polymers, and to crosslink prepolymer systems. These reactions usually require the presence of photosensitizer species in order to take place and electron donors, such as tertiary amines, have been shown to increase the rate of reaction. Many of these sensitizer systems have been reported for a large variety of polymerizations, but there appears to have been little attempt to relate activity to chemical structure using comparable conditions. The present study has statistically evaluated the activity of a number of sensitizers and amines over a range of concentrations by use of methyl acrylate as a common monomer. Other monomers have also been studied. Polymerization rates have been measured using refractometry. Relatively low intensity lamps have been used for irradiation to enable the polymerizations to proceed at a slow enough rate for measurements to be conveniently made. The results could be extrapolated to application of high intensity ultraviolet radiation as used in rapid polymerizing formulations.