In this note, it is shown that, given a ? -institution ℐ = ?Sign, SEN, C ?, with N a category of natural transformations on SEN, every theory family T of ℐ includes a unique largest theory system of ℐ. satisfies the important property that its N -Leibniz congruence system always includes that of T . As a consequence, it is shown, on the one hand, that the relation ?N () = ?N (T ) characterizes N -protoalgebraicity inside the class of N -prealgebraic ? -institutions and, on the other, that all N -Leibniz theory families associated with theory families of a protoalgebraic ? -institution ℐ are in fact N -Leibniz theory systems. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)