Theophyllinederivatives with several groups linked at the 7‐position were synthesized and their pharmacological activities were studied on guinea pig. Relaxant action in the tracheal muscle was increased in comparison with that of theophylline when the 3(2H)‐pyridazinone system was linked to 7‐(2‐ethyl)‐theophylline through the piperazine ring, but decreased when the 7‐(2‐ethyl)‐theophylline was linked