Résumé : The differences in width and in deposited energy between electromagnetic and hadron showers developed by 18.5 and 38 GeV/c pions and electrons in a combined hodoscope detector composed of a GAMS-type electromagnetic calorimeter and a modular hadron calorimeter allow to reject pions or electrons to a level ≪ 0.1% keeping a detection efficiency larger than 90% when the other particle is selected. The hadron calorimeter helps to efficiently reject background in studies of multiphoton decays of neutral mesons with GAMS. © 1989.