Pulmonary rejection and infection are the most important complications after lung transplantation. To evaluate the diagnostic value of pulmonary function testing for early detection and discrimination of these complications, seven heart-lung recipients were examined. The diagnosis of each complication was confirmed by clinical and laboratory findings including transbronchial biopsies and bronchoalveolar lavage. Eight episodes of rejection, ten episodes of viral infection and six episodes of bacterial pneumonia were analyzed. Pulmonary rejection was associated with a significant fall in the FEV1/IVC% and the FEF50%. In viral infection, the most impressive finding was a reduction in the DCO, whereas no obstructive or restrictive airway dynamics were observed. During bacterial pneumonia, pulmonary function measurement revealed a decrease in IVC without signs of obstructive airway dynamics. Adequate treatment resulted in reconstitution of pretreatment values. Assessment of lung function provides valuable information for the diagnosis of pulmonary complications following HLTx.