To determine whether regurgitation might be a factor in the pathogenesis of apnea in certain infants, we compared the frequency of short and prolonged apnea immediately following regurgitation to that during control periods. Ten infants (nine preterm and one term) with histories of frequent regurgitation and also apneic spells were studied for 2 to 3 hours by monitoring nasal airflow, abdominal respiratory movements, electrocardiogram, pharyngeal pH, and pharyngeal pressure. In six of these infants additional observations were made without the intrapharyngeal recording devices. Fourty-four episodes of regurgitation were observed. Both prolonged apnea (P less than 0.05) and short apnea (P less than 0.01) occurred much more frequently during regurgitation than during the control period; however, the majority of prolonged apneic spells observed were unassociated with regurgitation. The increased frequency of apnea during regurgitation was not related to the presence of intrapharyngeal recording devices. Although nasal regurgitation was frequently associated with short apnea, no prolonged apnea was observed during the seven episodes of nasal regurgitation observed. The 14-fold increase in prolonged apnea frequency immediately following regurgitation supports the hypothesis for a causal relationship between apnea and regurgitation.