Hirschsprung's disease in the newborn period has a bad prognosis due to the high mortality rate caused mainly by enterocolitis. It has been shown that the incidence of enterocolitis diminishes with the precocity with which diagnosis is made. All diagnostic methods have problems in the neonate. We intent to investigate the anorrectal manometry in the neonate using a probe devised and built by us. The hypothesis we try to prove is that the rectoanal reflex is present in all newborn, having no relation with age, length of gestation period, nor weight. The characteristics of the probes used allowed long recording sessions without any sedation of patients. The validity of this technique is unquestionable from the view of the reliability of the recordings independently of the weight, gestational age and birth age of the infants.