Anorectal manometry with perfused side opening catheter was carried out in 86 normal infants and children, 9 infants with Hirschsprung's disease, and 10 children with idiopathic chronic constipation. Studies on pressure volume curve of the rectum and rectal compliance were carried out in 37 normal infants and children, 4 infants with Hirschsprung's disease, and 10 children with idiopathic chronic constipation. Decreased basal rhythmic contraction of the anal canal, absent recto-anal reflex, steep elevation of pressure volume curve of the rectum, and low rectal compliance were characteristic of infants with Hirschsprung's disease. Resting pressure profile of the anorectum, recto-anal reflex, pressure volume curve of the rectum, and rectal compliance were normal in chronically constipated children without megarectum, whereas remarkably high rectal compliance was characteristic of those with megarectum.