In 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. agalactiae and 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 [MIC(50)], 0.5 mg/liter; MIC(90), 1 mg/liter, MIC range, 0.25 to 4 mg/liter).