To evaluate the incidence of vancomycin tolerance among Streptococcus pneumoniae isolates, we performed killing curve studies with 633 isolates. The penicillin MIC was > or = 0.12 mg/liter for 481 (76%) of the isolates. All strains were susceptible to vancomycin. Killing curve studies were performed with a vancomycin concentration of 2.5 mg/liter. The Tupelo strain was used for quality control. No vancomycin-tolerant strain was detected.