SummaryThe study of the susceptibility of 100 strains of Staphylococcus aureus to Tetracycline and Minocycline reveals two different types of resistance for these two antibiotics. Tetracycline susceptibility, when present, is unequivocal. In the contrary, many strains are moderately sensitive to Minocycline ; taking into account the blood levels achievable, this suggests that Minocycline could hardly be an effective drug against such strains.