The steady-state fluorescence technique was used to study the polymerization rate and the autoacceleration due to the gel effect in free-radical polymerization of methyl methacrylate. Pyrene was used as a fluorescence probe for the in situ polymerization experiments. The times required for the onset of the gel effect were recorded for various polymerization temperatures. A simple kinetic model was used to validate the experimental data. The results show that the fluorescence technique can be used to follow the onset of the gel effect and the activation energy during the polymerization processes. (C) 1997 Elsevier Science Ltd.