Resistance to streptothricin was studied in bacteria with different resistance mechanisms. The laboratory-induced streptothricin-resistant mutant E. coli A19 Stcr 2/2/1 showed a high level of cross-resistance to aminoglycosides and other miscoding inducing antibiotics. In contrast, aminoglycosid-resistant E. coli strains with plasmid-determined aminoglycoside modifying enzymes were sensitive to streptothricin. Enzymatic inactivation of streptothricin by acetylation was demonstrated for the streptothricin producing Streptomyces noursei, strain NG13. This strain showed no cross-resistance to miscoding inducing aminoglycosides.