Monoclonal antibodies against partially purified adenylyl cyclase from bovine brain cortex were raised in mice. Three types of antibody were obtained. Type 1 was specific for the calmodulin-sensitive enzyme. Type II also recognized this enzyme, but recognized the calmodulin-insensitive enzymes from a variety of species and tissues as well. Type I antibodies precipitated their antigens in both the native and denatured forms, while type II strongly favored the denatured forms. Type III antibodies precipitated adenylyl cyclase activity, but as shown by Western blot analysis, were directed against 38-kDa and 45-kDa glycoproteins. The 38-kDa protein was identified as synaptophysin.