A therapy directed toward slowing and regularizing the ventilatory pattern was compared with a partial-treatment, comparison procedure for individuals with somatic and psychological symptoms attributable to hyperventilation episodes (i.e. hyperventilation syndrome). Comparing repeated measures between a pretreatment baseline session and a post-treatment followup, we found that the experimental therapy, in contrast to the comparison procedure, produced a greater number of, and more extensive, improvements in psychological, symptom complaint and ventilatory dimensions. Results also suggest changes in central respiratory control mechanisms as a consequence of treatment.