This study has investigated the effect of interrupting nasal continuous positive airway pressure (nCPAP) therapy on 10 obstructive sleep apnoea (OSA) patients (nine male, one female) (53.6 +/- 7.3 years) treated over 2 years. The effect of nCPAP interruption was determined by variations in sleep counts and gasometric values during five consecutive nights. On the first night, the patient used his habitual nCPAP. On the remaining nights, nasal nCPAP was not applied. The apnoea-hypopnoea index (AHI) was found to increase significantly in the second night, attaining a similar level to that of the basal study (2 years ago). SaO2 minimum decreased and PaCO2 increased in the second night with respect to the first night. The interruption of nCPAP therapy in OSA patients treated over a long period of time increases the sleep counts and impairs the gasometric parameters. Consequently, any change in nCPAP time therapy must be checked to avoid negative effects.