The effectiveness of several basic compounds for testing silica-based stationary phases was reviewed by applying them to recent columns for reversed-phase HPLC. Most octadecylsilylated (C18) stationary phases, prepared as a base-deactivated material from high-purity silica gel with endcapping, provided excellent peak shape and column efficiency for the bases including benzylamine and amitriptyline that once caused problems and were subsequently employed for testing silanol activities. However, a cyclic tertiary amine, dextrometorphan, was eluted as an acceptable peak from only a few columns at neutral pH. Such a more sensitive probe is expected to contribute to further improvement of the stationary phase for reversed-phase HPLC.