Experiments were designed to compare cellular profile of bronchoalveolar lavage following induced bacterial infection after lung allograft. After single lung allotransplantation, dogs were immunosuppressed with standard triple therapy and divided into three groups: Group I (n=4), maintained on immuncsuppression as controls; Group II (n=7), triple therapy was discontinued to induce rejection; Group III (n=6), infection was induced by bronchoscopic inoculation of E. coli at day five, immunosuppression was maintained. At day nine, bronchoscopic lavage was performed in the transplanted lung. With infection total cell count in the lavage was elevated compared to lavage from control and or rejecting animals (4983 ±1704 vs 900 ±333 and 740 ±187, respectively). Differential neutrophil count was elevated with infection compared to control and rejection (83 ±2 vs 36 ±13 and 74 ±2, respectively). However, differential lymphocyte count was decreased with infection compared to control and rejection (3 ±2 vs 13 ±3 and 8 ±2, respectively). Differential monocyte/macrophage count was decreased with infection compared to control (14 ±1 vs 49 ±15), but comparable to rejection (17 ±4). These results suggest that cellular infiltration in bronchoalveolar lavage reflects the underlying pathological process in the allografted lung.