In vitro activity of four fluorinated quinolones: pefloxacin, norfloxacin, ciprofloxacin, ofloxacin were determined against various clinical isolates of mycobacteria. The method of agar dilution was used, seventy strains of ten species were tested: Mycobacterium tuberculosis (25), Mycobacterium bovis (5), Mycobacterium africanum (2), BCG (5), Mycobacterium kansasii (6), Mycobacterium marinum (5), Mycobacterium avium (11), Mycobacterium xenopi (6), Mycobacterium chelonae (3), Mycobacterium fortuitum (2). Except for Mycobacterium avium and Mycobacterium chelonae (CMI 100% greater than 8 mg/l) fluorinated quinolones showed activity against tested mycobacteria (CMI 100% less than or equal to 8 mg/l). Ofloxacin and ciprofloxacin where found to be the most active. Their activity against the different strains of Mycobacterium tuberculosis was unrelated to their susceptibility or resistance to the antituberculous drugs.