A method of assessing the extent of cure of epoxy resins is described. Fluorescent dyes are added to the uncured material. Fluorescence in response to UV excitation increases with the viscosity and thus extent of cure, and was measured with a spectrophotometer. The technique is suggested as a method of monitoring in situ. (Editors' note: the assumed reversibility of some epoxies may relate to extent of cure.) -- AATA