Although inhalation technique is more physiological, direct intratracheal instillation has often been performed to assess toxicity in the lung. During intratracheal instillation, animals are narcotised. For rodents, short-acting anaesthetics, which suppress reflexes for a minimal period of time and allow the animal to recover quickly and regain normal respiration, are preferred. Halothane, metaphane, enflurane and isoflurane are inhaled anaesthetics frequently used. The deeply narcotised animal is positioned on an angled restraining stand, its throat illuminated by a light source. The test substance is suspended in an appropriate vehicle and instilled into small laboratory rodents usually by inserting a catheter or needle trans-orally into the tracheal lumen (Brain et al, 1976; Saffiotti et al, 1968, 1972).