Nineteen men, aged 20 to 50 years, were treated in a double-blind crossover study comparing oxygen v air inhalation at 6 L/min via nonrebreathing face masks for 15 minutes or less, for up to six headaches. Patients scored their own degree of relief for each treatment as none, slight, substantial, or complete relief. The average (+/- SE) relief score for all oxygen-treated patients was 1.93 +/- 0.22 out of a possible total score of 3.0, and for air the treatment relief score was 0.77 +/- 0.23. This difference is highly statistically significant by an analysis-of-variance F test; it documents that patients with cluster headache can benefit from oxygen inhalation during acute attacks.