SummaryWe report the results of 29 diagnostic bronchofibroscopies performed from January to October 1985 in 25 immunocompromised Patients with haematologic diseases, presenting with radiographic pulmonary infiltrates of unknown aetiology.In 13 cases (13 fibroscopies) specific diagnoses were obtained: infection in 11 cases and tumoral invasion in 2 (non-Hodgkin lymphoma). This gives a specific diagnostic yield of 45 % per fibroscopy and of 52 % per patient. The infections were due to fungi in 5 cases (Candida albicansandkrusei, 3 Torulopsis glabrata), bacteria in 3 cases (Serratia marcescens, Streptococcus pneumoniae, Pseudomonas aeruginosa), fuberculosis in 2 cases, andHerpes simplex virus1 case. All investigatory procedures used at fibroscopy (virus isolation, cultures, cytohistology) have contributed to the diagnosis..12 cases (16 fibroscopies) a specific diagnosis could not be made. Infection was suspected in 8 cases (11 fibroscopies), but all‘ibroscopic investigations were negative. In 4 cases fibroscopy provided only atypical results (mostly fibrosis on histology), but other investigations provided a diagnosis: graft-versushost-disease in 2 cases and non-Hodgkin‘ymphoma in 2 cases. A specific fibroscopic d’agnosis often led to an adaptation of therapy; however, survival remained poor.Fibroscopy was well tolerated and caused no serious complications such as respiratory distress, major bleeding or pneumothorax. In no case repeated fibroscopy was useful.