Pulmonary toxic effects subsequent to intravenous injections of bleomycin in cancer therapy have well been demonstrated. In order to prevent the acute pathological pulmonary manifestations of the treatment, it is necessary that the patient be submitted to repeated controls of the lungs. As yet, the efficiency of the current diagnostic procedures for detecting the lesions dues to bleomycin injections is not clearly demonstrated. The authors present the results of a comparative study on the effectiveness of radiological and scintigraphic examination of the lung in detecting toxic side-effects of bleomycin. Both procedures were used repeatedly on rabbits, before, during and after the bleomycin treatment. The findings are discussed on the basis of the macroscopic and histological examination of the lungs. The results demonstrate that pulmonary scintigraphy with radioactive macroaggregates is more sensitive than radiography in detecting the early lesions of the lungs after bleomycin treatment.