As a result of clinical heart-lung transplantation, the lungs are denervated below the level of the tracheal anastomosis. It has been questioned whether afferent vagal reinnervation occurs after surgery. Here we report the cough frequency, during inhalation of ultrasonically nebulized distilled water, of 15 heart-lung transplant patients studied 6 wk to 36 months after surgery. They were compared with 15 normal subjects of a similar age and sex. The distribution of the aerosol was studied in five normal subjects using 99mtechnetium diethylene triamine pentaacetate (99mTc-DTPA) in saline. In seven patients, the sensitivity of the laryngeal mucosa to instilled distilled water (0.2 ml) was tested at the time of fiberoptic bronchoscopy by recording the cough response. Ten percent of the aerosol was deposited onto the larynx and trachea, 56% on the central airways, and 34% in the periphery of the lung. The cough response to the aerosol was strikingly diminished in the patients compared with normal subjects (p less than 0.001), but all seven patients coughed when distilled water was instilled onto the larynx. As expected, the laryngeal mucosa of heart-lung transplant patients remains sensitive to distilled water. However, the diminished coughing when the distilled water is distributed by aerosol to the central airways supports the view that vagal afferent nerves do not reinnervate the lungs after heart-lung transplantation, up to 36 months after surgery.