The aminoglycoside-modifying enzymes present in the first 120 clinical isolates harboring extended-spectrum beta-lactamases isolated in Spain were studied. Most of these isolates (84%) were gentamicin resistant. The enzymes most frequently associated and cotransferred with SHV-2 or TEM-type beta-lactamases were AAC(3)V, APH(3"), and APH(3')I.