Clinically relevant apneas, which are common in preterm infants, may adversely affect later neuropsychological condition in this group of patients. Pharmacotherapy to stimulate respiratory functions may be unsuccessful. Polygraphic recording may help in the differential diagnosis of these clinically relevant events. Twenty-nine preterm neonates born before 36 weeks of gestational age were examined using polygraphic recording (respiration--two channels, perioral electromyography, oxygen saturation, heart rate, electroencephalography, electrocardiography, electrooculography). The examination was ordered by the attending physician after an unsuccessful treatment of apnea by Aminophylline, and it should contribute to the clarification of the causes of these events. In the course of the polygraphic examinations, altogether 63 episodes were recorded during which the pulse oximeter alarm signal was set off. In 42 cases, the alarm signal was set off in events during which SaO(2) fell below 85%. In the remaining 21 cases, the alarm signal was set off in episodes during which early bradycardia below 90/min occurred. The onset of apnea was very often associated with the phasic increase of the perioral electromyography and with electroencephalography arousal reaction. Because of suspicion that these apneas may be triggered by episodes of gastroesophageal reflux, the interruption of the Aminophylline treatment and setting up an antireflux regimen were recommended. These therapeutic measures had a positive effect: The frequency of alarm signals decreased within 48 h by a statistically significant 50%. In cases where the pharmacotherapy of apnea by stimulation of respiratory functions is not successful, differential diagnostic analysis should be performed. Polygraphy may contribute to the clarification of the causes underlying clinically relevant apneas in a view of newly described polygraphic signs. It is feasible to suspect, based on these signs, that gastroesophageal reflux is the cause for clinically significant apneas in that case.