Some pyrrole derivatives were found to be catalytically unhydrogenable during the systematic investigation of heterogeneous catalytic hydrogenation of several pyrroles. These compounds cannot be hydrogenated neither over precious metal (Pd, Ru, Rh) nor over Raney nickel catalysts, even under extreme reaction conditions (130degreesC, 100 bar), in liquid phase. These now and unexpected results are reported. (C) 2002 Elsevier Science B.V. All rights reserved.