A new method has been found for monitoring polymerization reactions in situ and in real time. The first moment of fluorescent emission, = SigmaI(F)(v)v/SigmaI(F)(v) is calculated from fluorescence spectra as a function of polymerization time and can be successfully correlated with the conversion of functional groups, obtained by an independent technique, with a very low level of experimental scatter. The statistical analysis of the method has been performed; some simple computer experiments allowed to study the influence of the most important experimental variables yielding the confidence interval of as a function of the noise to signal ratio. This method was applied with stepwise polyaddition (epoxide curing) and polymerization by free radical mechanisms. 5-Dimethylaminonaphthalene-1-sulfonamide derivatives, 4-dialkylamino-4'-nitrostilbene and pyrene were used as probes and/or labels. Other methods reported in the literature have been applied also. Comparison with them reveals that the first moment method is more reliable for monitoring polyaddition reactions.