The variation of blood pressure was investigated by power spectrum analysis in 12 patients with severe sleep apnea with and without nCPAP-therapy. In the baseline findings systolic and diastolic variation consisted of mainly two types of pressure oscillations: Swings of slow frequency (0-0.06 Hz) in tight association with the periodicity of breathing disorder and arousal and extensive respiratory pressure waves (0.2-0.5 Hz) due to the increased intrathoracic pressure changes during breathing efforts with partial or complete obstruction of the upper airway. In general systolic was higher than diastolic variation and the contribution of slow pressure oscillations was considerably bigger than that of respiratory waves. Sufficient nCPAP-therapy resulted in a decrease of the mean pressure and in a clear reduction of systolic and diastolic variation in which both types of pressure waves were diminished in a similar manner. At last there was a higher proportion of pressure waves in the frequency range of the Mayer-waves (0.06-0.2 Hz) with nCPAP-therapy.