The response of two strains of amoebae, A. proteus and A. discoides, to varying concentrations of neomycin and kanamycin has been investigated. The two strains showed no difference in their response to kanamycin. Between 0.4-1.0 μg/ml of neomycin, A. proteus was more sensitive than A. discoides. The heterotransfers between these strains showed that both nucleus and cytoplasm areable to confer lowered sensitivity to neomycin. Examination of clones derived from microinjection of A. discoides cytoplasm into A. proteus showed that lowered sensitivity to neomycin could be transferred. © 1969.