The minimal inhibitory concentrations (MICs) of nine antibiotics were determined by agar dilution on 123 strains of Streptococcus pneumoniae (65 penicillin sensitive, 42 intermediate resistant and 16 resistant). The antimicrobial agents tested were penicillin G, clindamycin, trospectomycin, daptomycin, teicoplanin, cefpodoxime, ciprofloxacin, ofloxacin and vancomycin. Of these, daptomycin, teicoplanin and vancomycin demonstrated the greatest in-vitro activity against penicillin-resistant strains (MIC90s less than or equal to 0.25 mg/l). Ciprofloxacin, ofloxacin and trospectomycin had equivalent activities unaffected by penicillin-susceptibility (MIC90 of both quinolones 2.0 mg/l, and of trospectomycin 4.0 mg/l). Cefpodoxime was also active in vitro against all strains (MIC90 2.0 mg/l), but MICs increased with increasing penicillin-MICs. Most penicillin-susceptible strains were susceptible to clindamycin, but many penicillin intermediate resistant and resistant strains were resistant to this drug. Results of this study indicate that several newly introduced and experimental antibiotics have potential in the treatment of infections caused by resistant strains of Str. pneumoniae.