The minimum inhibitory concentrations (MICs) of vancomycin and teicoplanin were determined for 32 coagulase-negative staphylococci strains recovered from blood specimens from pediatric intensive care patients. All the strains were susceptible to vancomycin (MIC less than 4 mg/l). Sixteen strains were susceptible to teicoplanin (MIC less than 4 mg/l) and the sixteen remaining strains exhibited intermediate susceptibility, with MICs of 8 mg/l (10 strains) or 16 mg/l (6 strains). Inhibition zone diameters seen with vancomycin during agar diffusion susceptibility testing were consistently greater than 17 mm. Inhibition zones obtained with teicoplanin were 17 mm or more in diameter for 30 strains and under 17 mm in diameter for 2 strains. For 14 strains (44%), agar diffusion testing failed to detect the decreased susceptibility to teicoplanin revealed by MIC determinations. The agar diffusion method does not seem reliable for the determination of in vitro susceptibility to teicoplanin.