This study was carried out in the tuberculosis laboratory of the Institut National d'Hygiène in Rabat, Morocco, in 1997. The aim was to determine the percentages of drug-resistant strains by using 150 antibiograms. Six antimycobacterial medications were used as tuberculosis treatment: isoniazid (INH), streptomycin (STM), rifampicin (RIF), ethambutol (EMB), kanamycin (KAN) and p-amino-salicylic acid (PAS). The cultures were plated onto a simple agar (Lowenstein-Jensen) plate containing different concentrations of drugs. This test demonstrated the presence of major antimycobacterial (INH, RIF, STM)-resistant strains of Mycobacterium tuberculosis in the following percentages respectively: 34.6 per cent, 33.1 per cent and 26.1 per cent and 80 per cent, 70 per cent and 40 per cent in the case of atypical mycobacteria. The association of INH/RIF showed the highest percentage (27.6 per cent) for Mycobacterium tuberculosis and 70 per cent for atypical strains, whereas, when we associate INH/RIF/STM, the resistance rate becomes 17.69 per cent for Mycobacterium tuberculosis and 25 per cent for atypical mycobacteria. The resistance in question was a secondary or acquired resistance because the tested strains were isolated from patients who had not responded to standard tuberculosis treatment.