Between November 1983 and August 1993, The Toronto Lung Transplant Program performed 153 transplantations in 144 recipients: 53 single-lung transplantations (SLT) and 100 double-lung transplantations (DLT). Thirty-eight open lung biopsies (OLBs) were done in 32 (22% of all recipients): 19 in SLT (36% of SLT) 12 in DLT (12% of DLT), and 1 in a patient who had a SLT and then a double retransplantation. Six recipients underwent OLB twice: 1 DLT, 3 SLT, and 2 who had OLB both before and after retransplantation. Indication for 11 early OLBs (< or = 45 days postoperative) was persistent parenchymal infiltrates. Indications for 27 late OLBs (> 45 days postoperative) included progressive radiologic disease with clinical findings or progressive loss of pulmonary function (18), persistent poor graft function (3), mass or nodules (3), persistent infiltrates without functional loss (2), and persistent lymphocytosis in bronchoalveolar lavage (1). Open lung biopsy confirmed a previous clinical or pathologic diagnosis in 11, suggested a diagnosis in 2, yielded nonspecific information in 16, and provided different diagnosis in 9. New diagnosis that changed therapy was made in 1 of 11 early OLBs and in 8 of 27 late OLBs. These 9 diagnoses included in SLTs: bronchiolitis obliterans (2), bronchiolitis obliterans organizing pneumonia (1), malignant lymphoma (1), and chronic vascular rejection (1) in SLT, and bronchiolitis obliterans organizing pneumonia (3) and Burkholderia cepacia infection (1) in DLT. We conclude that OLB is of little value in the perioperative period but yields useful information in approximately 30% of patients when performed late.