The purpuse of this study was to compare and evaluate two methods, namely, BACTEC anda agar proportion methods, in determining the in vitro susceptibility of Mycobacterium tubercularis complex to major antituberculosis drugs (isoniazide=INH, ritampicin=RIF, ethambutol=EMB and STM=streptomicin). The positivity of acido-resistant bacilli among 104 concentrated clinical specimens was 36.54%. With the BACTEC method, 59 (56.73%) of 104 strains were resistant to at least one drug; 26 (25%) of them resistant to INH, 11 (10.58%) to RIF, 19 (18.27%) to EMB and 3 (2.89%) to STM. Six (5.76%) strains were resistant to two and four (3.84%) strains were resistant to three drugs. With agar proportion method, 67 (64.42%) of 104 strains were resistant to at least one drug; being 25 (24.04%) of them resistant to INH, 11 (10.58%) to RIF, 27 (25.96%) to EMB and 3 (2.89%) to STM. Seven (7.69%) strains were resistant to two and five (4.80%) strains were resistant to three drugs. There were no strains resistant to all of the four drugs with both methods. When the two methods were compared, the agreements for INH, RIF, EMB, and STM were as follows: for INH 99%, for RIF 100%, for EMB 92.3% and for STM 100%. BACTEC method reguires less laboratory work, is faster and gives more standardized results compared to agar proportion method, and it can be used safely for routine susceptibility tests of first-line antituberculosis drugs.