Abstract Although the lethal action of streptomycin (SM) may not be related to its effect on the protein biosynthesis, it appears clear that SM influences ribosomal function through inhibition or miscoding ( Davies et al. , 1964 ). The target of SM action is apparently 30S ribosomal subunits ( Cox et al. , 1962 ). Thus, SM inhibits the specific binding of phenylalanyl tRNA to the complex of poly U-30S ribosomal subunits ( Kaji et al. , 1966 ). On the other hand, no miscoding effect was observed with the binding of aminoacyl tRNA to 30S ribosomal subunits while miscoding takes place with 70S ribosomes ( Kaji, 1967 ) suggesting that 50S ribosomal subunits may play some role for the miscoding by SM. In our preceding communication we reported that one molecule of dihydrostreptomycin (DHSM) binds to a 30S ribosomal subunit. In this paper we report that proteins of core particle, but not RNA, isolated from SM-sensitive 30S ribosomal subunits are responsible for the binding of 3H-DHSM.