The effects of elastase-induced emphysema on vagal pulmonary reflexes were studied in seven rabbits, given 600 IU of porcine pancreatic elastase intratracheally (E group), and eight untreated rabbits (U group) under pentobarbital anaesthesia. The presence of emphysema was confirmed by histological and pathological criteria and by documented changes in lung mechanics seven months after treatment. The strength of the Hering-Breuer inflation reflex (HBIR), indicative of pulmonary stretch receptor excitability, was unchanged in the U group, but was significantly increased in the E group at inflation volumes greater than the tidal volume (VT) range, as she slope of the curve relating HBIR to inflation volume was significantly steeper (0.40 vs 0.22 ml-1; p less than 0.05). The early ventilatory response (first 3 breaths) to right atrial injections of phenyldiguanide (20 and 30 micrograms X kg-1 i.v.) was used as an indication of the excitability of lung receptors with non-myelinated vagal afferents. This response, characterized by a significant decrease in expiratory duration (TE) without effect on VT or inspiratory time (TI), was not significantly different between the E and U groups. The overall pattern of breathing in the E group showed a significant decrease in VT associated with an increase in TI.