The susceptibility of groups A, C, and G streptococci isolated from pharynx or skin in two northern Canadian native communities during a one year study of the epidemiology of streptococcal infection was determined for penicillin, erythromycin and clindamycin using an agar dilution method. Organisms studied included 725 group A, 82 group C, and 184 group G streptococci. All organisms were susceptible to penicillin (minimum inhibitory concentration [MIC] range less than 0.004 to 0.015 μg/mL; MIC₉₀ 0.015 μg/mL) and clindamycin (range 0.007 to 0.06 μg/mL; MIC₉₀ 0.06 μg/mL) with no differences observed between streptococcal groups. For erythromycin, groups A and C were generally susceptible (range less than 0.007 to 0.030 μg/mL; MIC₉₀ 0.03 μg/mL; and range 0.007 to 1.0 μg/mL; MIC₉₀ 0.06 μg/mL, respectively). Group G was less susceptible (range 0.007 to greater than 2.0 μg/mL; MIC₉₀ greater than 2.0 μg/mL) with 38% of all isolates having an MIC greater than or equal to 1 μg/mL. On review of group G isolates, 100 of 100 from one community were susceptible (MIC less than 0.007 to 0.03 μg/mL) and 73 (87%) of 84 from the second community were resistant. All resistant strains tested were type T16. These data suggest that erythromycin-resistant group G streptococci may occur with high prevalence in certain populations and that patterns of antimicrobial susceptibility in isolated communities may be highly community-specific.