Medroxyprogesterone acetate (MPA) could change the frequency and/or duration of disordered breathing events (DBEs) in patients with the obstructive sleep apnea (OSA) syndrome by altering pharyngeal muscle function relative to diaphragm and external intercostal function. Ten male patients with OSA syndrome underwent an initial polysomnogram with monitoring of EEG, EOG, myohyoid EMG, oral and nasal airflow, abdominal and thoracic movement, and SaO2. The patients were then entered into a randomized, double-blind crossover study using MPA, 150 mg/day, and MPA placebo. Each patient took tablets for one week and then had a second polysomnogram. After a three week washout, the patient again took tablets for a week prior to the third and final sleep study. There was no significant difference between drug and placebo for DBE time (expressed as a percentage of sleep time), DBE frequency, DBE mean duration or mean fall in O2 saturation during DBEs. We conclude that treatment with MPA does not alter indices of severity of the OSA syndrome.