"The Devils of Loudun" is scored for enormous musical forces, including nineteen soloists, five choruses (nuns, soldiers, guards, children, and monks), orchestra, and tape. The orchestra itself is of a great size too, making use of a very particular blending of instruments. The orchestra is composed of four flutes (alternating two piccolo and one alto), two English horns, an E♭ clarinet, a contrabass clarinet, two alto saxophones, two baritone saxophones, three bassoons, a contrabassoon, six horns, four B♭ trumpets (alternating one D trumpet), four trombones, two tubas, percussion (4 players), twenty violins, eight violas, eight celli, six basses, harp, piano, harmonium, organ, and bass electric guitar. The percussionists play timpani, military drum, friction drum, bass drum, slapstick, five wood blocks, ratchet, guiro, bamboo scrapers, cymbals, six suspended cymbals, 2 tam-tams, 2 gongs, Javanese gong, triangle, tubular bells, church bell, sacring bells, musical saw, flexatone, and siren (not mentioned in the instrumentation list at the beginning of the score).