In order to produce specifically N-monoalkylated derivatives of aminoglycoside antibiotics of potential therapeutic values, we have developed an enzymatic reactor. This system uses the aminoglycoside acetyltransferase as catalyst and acetylcoenzyme A as acetyl donor. The immobilization of one aminoglycoside acetyltransferase on different resins has been studied. The coreticulation of this enzyme on DEAE cellulose in the presence of glutaraldehyde gives rise to an enzymatic resin of high efficiency. On the other hand, we have also studied the acetylation of coenzyme A in a simple manner. Acetylation occurs in a quantitative yield when the reaction is performed in the presence of polyvinyl-4 pyridine/divinylbenzene 2 per cent. These conclusions enabled to develop two types of acetylating reactors which give rise without purification to 3-acetyl gentamicin.