Abstract: An improved anaesthetical circuit with reverse inhalation is equipped with an injector of escaped anaesthetics connected by an inlet pipe to a valve in which a feeding pipe, leading from a source of constant flow, discharges a signal from a differential pressure indicator, being led into the valve through a conduit. The differential pressure indicator is fed from an energy source, on one hand, together with a conduit pipe leading from a drive pipe into the pressurized chamber of the differential pressure indicator, and a pipe leading from a connection pipe into the vacuum chamber of the differential pressure indicator, on the other hand. A connection pipe connecting an outlet pipe of the injector through a check valve with a rubber bag, which is arranged in a cylinder attached to the anaesthetical circuit.