SummaryDuring 8 months. From December 1986 unlil until July 1987. 200 clinical isolates of aminogly coside-resistani bacteria were tested for their production of aminoglycoside-modilying enzymes by means of a stepwise determination scheme, previously published.Enzymes, capable of inactivation of even the most stable aminoglycoside, were almost daily detectable and were closely, associated with nosocomial strains and nosocomial inlections.A higher restriction in antibiotic prescription is urgently required.