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Magnetic viscosity experiments were performed on Co-25-at.% Al fine-particle ferromagnets aged to peak magnetic hardness in the temperature range 298-573 K, and the results were found to obey the relationship M=A-S/sub 0/ ln t over a time interval of approximately 1 to 10/sup 3/-10/sup 4/ s. Coefficients of magnetic viscosity and susceptibility data are analyzed taking into account corrections for a finite demagnetizing factor, thus allowing the determination of the fundamental viscosity coefficient S/sub nu /=k/sub b/T/ nu M/sub s/, where nu is the activation volume. A linear fit and extrapolation of the temperature dependence of the maximum effective viscosity coefficients gives rise to nonzero intercepts, suggesting that interparticle interactions may influence magnetization reversal. The viscosity data are found to be in general agreement with a previously proposed modified Stoner-Wohlfarth coherent rotation model for predicting the levels of coercivity in these Co-Al alloys. >