The aim of this study was to determine the bacteriological properties of Corynebacterium diphtheriae strains isolated from bronchiole washing and cancer lesions. Bacteriological characterization included fluorescence/double sugar urease (King/DSU) screening tests, pyrazinamidase (PYZ), CAMP-reactions and radial immunodiffusion toxigenicity assay. Microorganisms produced fluorescence under ultraviolet light and were catalase positive; urea and aesculin hydrolysis negative; fermentation of glucose, maltose and sucrose and no fermentation of mannitol and xylose; PYZ and CAMP reaction negative. The API-Coryne system was used for bacterial preliminary identification at local hospital laboratory and produced numerical profiles 1010325 and 0010325 for sucrose positive C. diphtheriae var. mitis (nitrate positive) and C. diphtheriae var. belfanti (nitrate negative), respectively. The hemagglutination, adherence to glass and polystyrene assays evaluated adhesive characteristics. Strains were toxigenic and able to adhere to glass, polystyrene and human erythrocyte surfaces (titer 4). C. diphtheriae strains isolated from cancer patients expressed adhesive characteristics similar to strains isolated from immunocompetent hosts. Circulation of toxigenic C. diphtheriae continues to present a threat for children and adults including patients with cancer in hospital environment. Laboratories should remain alert to the possibility of isolation of diphtheria bacilli from adults with neoplastic disease.