Although transbronchial lung biopsy (TBBx) is widely acknowledged as the "gold standard" for diagnosis of acute rejection, controversy exists regarding the need to perform follow-up procedures. Over a 5-yr period, we performed 1,142 TBBx of which 173 were follow-up TBBx in 99 patients with pulmonary allograft rejection greater than or equal to International Society for Heart and Lung Transplantation (ISHLT) grade A(2) on initial TBBx. Rejection on the previous 173 TBBx was associated with lymphocytic bronchiolitis/bronchitis (LBB) > or = ISHLT grade B(2) in 82 patients and with cytomegalovirus (CMV) pneumonitis in 16 patients. Persistent rejection (> or = A(2)) was observed in 45 of 173 (26%) follow-up TBBx. Persistent B grade rejection (> or = B(2)) was present in 28 patients whereas new B grade rejection developed in 11 patients with > or = A(2) grade rejection. Rejection > or = B(2) was significantly (p < 0.05) associated with rejection > or = A(2). Fifteen follow-up TBBx showed new B grade rejection without signs of > or = A(2) rejection. A new diagnosis of CMV pneumonitis was made in 33 of 173 (19%). CMV pneumonitis occurred in 35 follow-up TBBx, four associated with > or = A(2) rejection and eight with > or = B(2) rejection. The overall incidence of bronchiolitis obliterans syndrome (BOS) in both groups was similar. Patients with persistent rejection on follow-up TBBx developed BOS at a median of 1.3 yr and median of 2.0 yr (p = not significant [NS]) posttransplantation. The practice of follow-up TBBx after rejection within 2 yr posttransplant is clinically useful as it provides valuable diagnostic information.