The purpose of this study is to determine the development of the resistance of hospital strains of Staphylococcus aureus to four aminoglycosides. Study observation was conducted in three periods with five years elapsed between each of them. The first pre-amikacin period (211 strains) lasted for 16 months. The second and the third post-amikacin periods lasted for 8 (53 strains) and 18 (230 strains) months, respectively. A total of 494 strains od S. aureus from 458 patients were examined. In the first period 40% strains were resistant to gentamicin, tobramycin and kanamycin. The percentage was increased to 90% in the second and the third period. No statistically significant difference among gentamicin, tobramicin and kanamicin in any of three periods was noticed. However, the frequency of the strains resistant to amikacin was increased from 36% in the second period to over 50% in the third. Nevertheless, statistically significant smaller number of strains was to be resistant to amikacin in respect to resistance to gentamicin, tobramicin and kanamicin (Fb = 54,84; p less than 0.01). The degree of resistance during the second and third period indicates a significant increase of MIC for gentamicin and amikacin (p less than 0.01). During this work phenotype exchange of strains took place. Hence, the phenotype TK from the first period was replaced with GTK during the second and with GKTA in the third.