en Microbiology and Anatomy Microbiology and Anatomy Original Research Original Research Tuberculosis remains a major public health problem in both developing and developed countries. Drug-resistant tuberculosis is an increasing health problem and serious challenge to tuberculosis (TB) control programs. Information about the susceptibility pattern of Mycobacterium tuberculosis isolates against anti-tuberculosis drugs is an important aspect to TB control. The objectives of the study were to evaluate the frequency of drug-resistance and to survey the nature of drug resistance among patients with pulmonary tuberculosis. Ninety-one M. tuberculosis strains were isolated from sputum samples of patients referred to Cerrhapasa Medical Faculty Hospital, Istanbul, Turkey, during a 9 month period. Drug susceptibility testing was performed to isoniazid (INH), streptomycin (SM), ethambutol (EMB) and rifampin (RMP) on Lowenstein-Jensen medium according to proportion method. Total resistance was identified in 40 of 91 patients (44%). The highest rate of primary resistance was to SM (21.1 %), followed by INH (15.8%), RMP (5.3%) and EMB (2.6%). Secondary resistance was most frequent to INH (33.3%), followed by SM (28.6%), RMP (23.8%) and EMB (14.3%). Multidrug resistance (MDR) was observed in 6 of the 91 cases (6.6%). Due to the high prevalence of drug resistance, particularly in developing countries, further studies should be conducted regularly to monitor resistance in these countries. 189 192 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-138&slc_lang=en&sid=1 SR MOADDAB 20031947532846003723 20031947532846003723 Yes From theDepartment of Clinical Microbiology, Istanbul University, Istanbul, Turkey A RAFI 20031947532846003724 20031947532846003724 No theResearch Center for TB and Pulmonary Diseases, Tabriz University of Medical Sciences, Tabriz, Iran.