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ABSTRACTIn a prospective multicenter study (1996 to 1999), 156 episodes of bacteremic streptococcal infections of neutropenic patients were evaluated. Streptococcus oralis(26.3%),S. pneumoniae(26.3%), S. agalactiae(11.5%),S. mitis(9%), and S. pyogenes(5.8%) were the predominant species. Four strains (2.6%) were found to be intermediately resistant to penicillin. One strain (0.6%) was found to be highly resistant to penicillin (MIC, 8 mg/liter). Reduced susceptibility to penicillin was detected among S. oralis(14.6%), S. mitis(7.1%), and S. pneumoniae(4.9%) isolates but was not recorded among S. agalactiaeand S. pyogenes. Resistance rates and intermediate resistance rates for other antimicrobials were as follows (all species): amoxicillin, 1.3 and 3.2%; erythromycin, 16 and 2.6%; clindamycin, 5.8 and 0%; ciprofloxacin, 1.9 and 7.7%. Quinupristin-dalfopristin showed good in vitro activity against most streptococcal isolates (MIC at which 50% of the isolates were inhibited [MIC50], 0.5 mg/liter; MIC90, 1 mg/liter, MIC range, 0.25 to 4 mg/liter).