Teicoplanin is a glycopeptide antibiotic structurally related to vancomycin. Both agents achieve their effect by binding to acyl-D-alanyl-D-alanine in the bacterial cell wall. The spectrum of activity of teicoplanin, like that of vancomycin, is restricted to Gram-positive aerobic and anaerobic bacteria. However, the activity of the two agents is not identical: teicoplanin is generally more active than vancomycin against streptococci and Gram-positive anaerobes; the two agents exhibit similar activity against Staphylococcus aureus (including methicillin-resistant strains); and vancomycin is more active tnan teicoplanin against some strains of coagulase-negative staphylococci. Inoculum size influences the activity of teicoplanin, and variations in activity against some strains of coagulase-negative staphylococci have been observed with different culture media. Resistance to teicoplanin and vancomycin is difficult to induce under laboratory conditions and the small increment in resistance that may develop is lost when the organisms are subcultured in the absence of the drugs.