Preeclampsia is the predominant cause of admissions to neonatal intensive care. The diurnal blood pressure pattern is flattened or reversed in preeclampsia. We hypothesized that snoring and partial upper airway obstruction contribute to nocturnal rises in blood pressure. We tested this hypothesis by controlling sleep- induced upper airway flow limitation and snoring with nasal positive pressure. Eleven women with preeclampsia underwent two consecutive polygraphic sleep studies with simultaneous beat-to-beat blood pressure monitoring. Average blood pressure for the night overall and in each sleep stage was calculated. Sleep architecture was similar on the two study nights. Sleep-induced partial upper airway flow limitation occurred in all patients in the initial study. Autosetting nasal continuous positive airway pressure (CPAP) applied at a mean maximal pressure of 6 +/- 1 cm H(2)O eliminated flow limitation throughout sleep on the treatment night. Blood pressure was markedly reduced on the treatment night [(128 +/- 3)/(73 +/- 3)] when compared with the initial nontreatment study night [(146 +/- 6)/(92 +/- 4)], p = (0.007)/(0.002). We conclude that partial upper airway obstruction during sleep in women with preeclampsia is associated with increments in blood pressure, which can be eliminated with the use of nasal CPAP.