A general structure, substituent and activity relationship of the following type has been fitted to the available ED₅₀ values of cyclic enaminone antiepilectic compounds. In this relationship "structure" was quantified by d, the distance measured between the carbonyl oxygen and the first atom of the aromatic ring. The "substituent" was quantified by Hammett substituent constant: (s). With the aid of the above function of two independent variables a new molecular structure was predicted by extrapolation that has shown about two orders of magnitude greater activity than the most active molecule in the original set with measured ED₅₀ values.