To understand further the association between high-level resistance to kanamycin and penicillin tolerance in group A streptococci, high-level resistance to kanamycin was transferred from a penicillin-tolerant group A streptococcal strain possessing a high-level resistance to kanamycin to a penicillin non-tolerant, kanamycin-susceptible group A streptococcal strain and transconjugants were examined for penicillin tolerance. Transfer of high-level resistance to kanamycin occurred at a frequency of 10(-6). Transconjugants carrying high-level resistance to kanamycin exhibited characteristics of penicillin tolerance. These findings suggest that the genetic basis for penicillin tolerance is related to that for high-level resistance to kanamycin in group A streptococci. Further studies are needed to characterize the transferable genetic element(s).