Tuberculosis has been and continues to be one of the most significant pathogens in term of human morbidity and mortality. The aim of the study is to evaluate the possible role of MOTT in treatment failure cases of pulmonary TB. The study includes 50 patients with treatment failure on bases of persistent positive sputum for more than 5 ms in Chest Department of Kasr El-Aini University Hospital, El-Abbasia Chest Hospital and Giza Chest Hospital between April 2002 to August 2003. Each of the 50 patients was subjected to: Full history taking, Clinical examination, Plain chest X-ray, Laboratory investigation including: CBC, fasting and PP blood sugar, ESR and hepato-renal profile.Sputum examination was done by Direct microscopic examination by ZN stain, Culture of mycobacterial tuberculosis using BACTEC TB system.-Using BACTEC NAP TB test on positive BACTEC culture to distinguish between TB complex and MOTT. Out of 50 patients proved to have persistent positive culture for mycobacteria, 39 patients (78%) had pulmonary infection with mycobacterium complex whereas 11 patients (22%) had pulmonary infection with MOTT. All the 11 patients were males and above 30 years. Three of them had associated medical problems and 6 had cavitary lesions.