The need for a standardized treatment protocol for multidrug resistant tuberculosis (MDR-TB) in resource-limited countries is being increasingly recognized. This single center, double blind, randomized controlled trial was designed to compare the time required for sputum culture conversion and extent of radiological improvement in cases of MDR pulmonary tuberculosis when isoniazid was included (both at a regular dose and at a high dose) as an adjuvant to the standardized second line of treatment. The study was designed to test the hypothesis that inclusion of high-dose isoniazid will enhance the effectiveness of the second line of treatment in cases of MDR-TB without significantly increasing the toxicity.