According to several investigations ano-rectal manometry is a valuable diagnostic test of Hirschsprung's disease. In order to yield accurate results it requires a quiet, calm child who cooperates. In the few instances when this is not possible, general anaesthesia may be desirable. Manometric recordings of the internal and sphincter activity were therefore performed in 15 healthy children when awake and during general anaesthesia. The tonic activity at rest was significantly reduced during anaesthesia. Relaxations of the internal sphincter in response to rectal distension were recorded in all children both when awake and during anaesthesia. They were, however, significantly less pronounced during anaesthesia. These findings strongly suggest that ano-rectal manometry in the diagnosis of Hirschsprung's disease may be performed with advantage during general anaesthesia if the child does not cooperate when awake.