New chemiluminescent compounds, stable in aqueous buffers, for use in biological assaying include acridanebased compounds and (1,2)-dioxetanes. Among the new acridanebased compounds are water-soluble acridanes, enhancer coupled acridanes, bis and trisacridanes as well as acridane-(1,2)-dioxetanes. Among the new (1,2)-dioxetanes are electron deficient group-containing dioxetanes and tethered bis-1,2-dioxetanes. The (1,2)-dioxetanes are useful as substrates for various enzymes. The acridanes can be admixed with an oxidizing agent. An aqueous buffer and, optionally, a stabilizer to form a substrate or reagent formulation useful for assaying, inter alia, HRP.