Tuberculosis was declared a global emergency by the World Health Organization (WHO) in 1993. The global problem of tuberculosis is further complicated by a substantial increase in drug resistant tuberculosis. Available data suggest that drug resistant TB especially multi drug resistant may represent a public health threat in areas with a high prevalence of tuberculosis, suboptimal TB control programmes and/ or HIV. The cure rate of these cases has been reported to be lower than for non-drug resistant TB with a failure rate of 44%. New therapies for MDR-TB have not been introduced since the fluoroquinolones in the 1970s. Strains of Mycobacterium Tuberculosis (M. tub.) in H resistant cases often contain mixture of susceptible & resistant organisms. Use of high dose H (16- 20 mg/kg) can eliminate susceptible & those with low level resistance4. This Study was done to evaluate the role of isoniazid (INH) at high & normal dosages as an adjuvant therapy in treatment of patients with persistent culture positive pulmonary tuberculosis despite 6 months of continuous first line antitubercular treatment and on culture at least resistant to isoniazid and rifampicin.