Tuberculosis (TB) is a major public health problem worldwide. About 3.8 million TB cases werernreported to WHO in the year 2001 from the 8.5 million estimated new cases. In Ethiopia thernestimated incidence of all cases of tuberculosis has reached 292 per 100000 populations. Thisrnfigure placed the country to rank 10th among the 22 high burden countries.rnThe resurgence of tuberculosis has been accompanied by high frequency of drug resistant strainsrnfrom all over the world. In most TB patients drug resistance predominantly arises as a result ofrnmultiple interruptions of treatment. To avoid this problem fixed-dose combinations (FDCs) tabletsrnare now recommended by WHO and IUATLD. However, in FDC formulations the bioavailabilityrnof the component drugs, and especially of rifampicin, may be reduced. Simple, rapid andrninexpensive methods of detecting drug resistant tuberculosis are also essential for effectiverntreatment.rnThis study has the objectives of assessing the prevalence of drug resistance among re-treatmentrncases after introduction of Three Fixed Dose Combination (3FDC) therapy for tuberculosis;rnevaluation of MTT assay for direct detection of rifampicin resistance and analysis of the RFLPrnpattern of the different TB strains. Single sputum samples were collected from 100 smear positivernre-treatment TB cases who attended St Peterâ€™s TB specialized Hospital between 21 December 2001rnand 15 October 2002. The sputum samples were cultured on Lowenstein- Jensen (LJ) media andrn7H9 broth. Drug sensitivity was done on 7H10 agar using the proportion method. Broth mediarn(7H9) supplemented with PANTA and Oleic acid Dextrose Catalase (OADC) were used for MTTrnassay. Formazan production was quantified by measuring the optical density (OD) at 570nm.rnRelative optical density unit (RODU) was calculated and resistance was defined as RODU> 0.5rnand susceptibility as RODU< 0.2.rnAmong the 89 culture positive isolates, 75 were tested for drug sensitivity pattern. Totally 58.7%rnof the isolates were resistant to one or more drugs. Isolates resistant and partially resistant tornisoniazid were found to be 42.7% and 6.7% respectively. Resistance to rifampicin was 33.3%.rnIsolates resistant and partially resistant to streptomycin were found to be 21.3% and 12%rnrespectively. The percentage of isolates resistant to ethambutol was 9.3% while 25.3% werernpartially resistant. Multidrug resistant isolates (MDR) were observed in 29.3% of the patients.rnPatients who had a history of treatment with 3FDC had a statistically significant higher rate ofrnresistance to isoniazid (P< 0.05) and rifampicin (P< 0.05) compared to those treated with looserndrugs. Direct MTT assay identified 30.7% isolates as rifampicin resistant and 69.3% as susceptiblernwithin three weeks of time. Comparing MTT assay to the proportion method resulted in 97.3%rnmatching. RFLP analysis of ten isolates showed the presence of eight unique patterns. Two isolatesrnshowed the dominant type of RFLP profile existing in Ethiopia. Contrary to our expectation,rnpatients treated with 3FDC regimen had more rifampicin and isoniazid resistant isolates than thoserntreated with loose drugs. This is a good indicator for a more systematic study to evaluate thernefficacy of the 3FDC drug formulation. There has been a marked increase in drug resistantrntuberculosis. Therefore, nationwide drug resistance surveillance with a larger number of samples isrnneeded to monitor drug resistance tuberculosis in the country