Quantitative assay of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities have been estimated in superficial rectal biopsies from 168 neonates or children suspected of having Hirschsprung's disease. The AChE activity made the diagnosis in 93% of the cases. The ratio AChE/BChE improved both the specificity and the sensitivity and confirmed the diagnosis on the first series of biopsies in 99% of the cases.