Halothane anesthesia was carried out on 6 horses for 120 min. At the first stage of the experiment, anesthesia was maintained with spontaneous ventilation (SV) that was eliminated by pancuronium at 60 min. and replaced by controlled ventilation (CV). This second part of the experiment was continued for 60 min. as well. Gasometric and volumetric dates were compared for the determination of changes caused by respiratory insufficiency usually progressing in anesthesia with natural breathing. In SV- -period, severe respiratory acidosis was developed as a result of hypoventilation of central origin. Intensified hypercapnia (РаСОз + 67.1 mmHg) was discovered at 60 min. of this part of anesthesia. CV-introduction (IPPV:f=ll, Vmin.—44 liter/min) improved the values of acid-base balance after 15 min. The above-mentioned parameters returned to the normal level after 30 min. of CV-application. The procedure with the use of CV, when anesthesia is still at work, allows to reverse consequences of the gas exchange disturbances in a short time providing a new and simple means of increasing the safety of a patient anesthetized by the conventional model of anesthesia.