Feasibility and reproducibility of home measurement of arterial oxygen saturation (SaO2) were evaluated in 14 clinically stable patients with cystic fibrosis (CF). Changes in SaO2 during sleep were compared to the clinical status and pulmonary function while awake to identify predictors of nocturnal oxyhemoglobin desaturation. Each patient was assessed by clinical score, spirometry, and arterial blood gas analysis within 72 hours of the overnight study. Eight patients were studied on more than one occasion to assess dependence of SaO2 on position and reproducibility of overnight studies. A pulse oximeter stored up to 8 hours of nocturnal SaO2 measurements in its memory. Off-line analysis of trend data provided the proportion of sleep with SaO2 less than 90% and less than 85%. We found that patients with daytime PaO2 less than 60 mm Hg spent greater than 80% of their sleep with SaO2 less than 90%, while those with PaO2 greater than 70 mm Hg spent less than 20% of the night with SaO2 less than 90%. Patients with daytime PaO2 of 67-70 mm Hg were desaturated to less than 90%, from 0 to 98% of the night. No consistent body position dependence of daytime SaO2 was found. Home measurement of SaO2 during sleep was reproducible, with a difference on two repeat occasions of 4% +/- 2 (mean +/- SEM) for %time with SaO2 less than 90% and 3% +/- 2 for %time with SaO2 less than 85%. The severity of hemoglobin desaturation during sleep could not be reliably predicted from clinical scores or awake pulmonary function.(ABSTRACT TRUNCATED AT 250 WORDS)