For rapid and low-cost detection of multidrug-resistant (MDR) Mycobacterium tuberculosis, we applied the nitrate reductase assay (NRA) using a liquid medium directly to sputum samples. A total of 179 sputum samples were analyzed by the NRA, and results were compared to those obtained by the indirect proportion method (IPM) as a standard reference. Out of 144 specimens for which comparable results were available, only one discrepant result was obtained: MDR by NRA but susceptible by the IPM. In total 56% of the results were obtained in 10 days by the NRA. NRA performed in liquid medium is rapid and inexpensive and can be easily implemented in low-income countries.