Since April 1973, 230 patients, who were suspected of Hirschsprung's disease, have been examined by rectal mucosal biopsy, barium enema and ano-rectal manometry. Their rectal mucosal specimens have been taken both from the regions 2cm upwards and just above the dentate line, and have been studied by means of acetylcholinesterase (AChE)-staining and hematoxylin-eosin (H-E)-staining. Specimens obtained by rectal full-thickness biopsies or operations were examined by means of AChE-staining, H-E-staining and silver-impregnation. Eleven out of the 230 patients were histologically diagnosed as hypoganglionosis. All rectal mucosas of hypoganglionosis showed a few small submucous plexus. According to the findings of nerve fibers, however, cases of hypoganglionosis were divided into three groups. The recognition of nerve fibers partially proliferated in rectal mucosa at the newborn age leads the diagnosis to type A. The type B is diagnosed as Hirschsprung's disease only through the recognition of proliferations of nerve fibers in rectal mucosa after the suckling age. In type C, no proliferation of nerve fibers can be recognized even after the suckling age. An accurate diagnosis of type C can be, therefore, made only through the examinations of myenteric plexus in full-thickness rectal specimen. On barium enema, a narrow segment was definite in 7 cases of hypoganglionosis, but was indefinite in the remaining 4 cases. The diseased segments of intestines were limited to the rectum or the rectosigmoid colon in 10 cases. Recto-anal sphincteric reflex showed an atypical reflex in 6 cases.(ABSTRACT TRUNCATED AT 250 WORDS)