Measurements were carried out of conductivity due to migrating charges as a function of extent of reaction for a series of epoxy-amine formulations. All systems were characterised by the reaction mechanism common to this generic group of materials and by an increase in the steady shear viscosity during reaction. The measured conductivity, however, followed one of three distinct patterns as a function of extent of reaction. Intuitively unexpected, and hence particularly interesting, was the observed increase in conductivity during reaction in several formulations. This communication marks the first time that such response has been reported in the literature. An explanation of the observed trends was offered in terms of an interplay between the contributions of extrinsic and intrinsic migrating charges to the overall (measured) conductivity. Without such information, all correlations between the measured conductivity and the major processing parameters (viscosity, extent of reaction) remain strictly batch-specific and empirical.