Long-term administration of zopiclone in 6 patients with severe chronic obstructive respiratory insufficiency with stable ventilatory function did not demonstrate any depressant action on respiratory blood gases recorded during the daytime and in ambient air. The sedative action of this agent was manifested by a modest decrease in ventilatory response parameters which, however, was not statistically significant. Polysomnographic recordings did not reveal any worsening of desaturation periods both with respect to incidence and amplitude. There was a non-significant trend towards an increase in the number of obstructive apnoea episodes without any notable ventilatory impact.