We studied in vitro bactericidal effects of netilmicin combined with other antibiotics, comparing with that obtained with other aminoglycosides combinations. We used strains of Streptococci and Gram negative rods tested versus 11 antibiotics : penicillin (P), ampicillin (Am), carbenicillin (Cb), cefalotin (Cth), cefazolin (Cfz), cefradin (Cfa), cefoxitin (Cxt), cefotaxime (CTX), erythromycin (E), pristinamycin (Pr), vancomycin (V). These were combined with streptomycin (Sm), tobramycin (To), amikacin (Ak), gentamicin (G) and netilmicin (Nl). First of all, we noted the high bactericidal power of Nl, whatever the strains tested. Against Streptococci, the activity of P + Nl and Am + Nl were equivalent or superior to that of P + G and Am + G. Among cephalosporins, we noted a synergistic effect of Ctx + Nl which did not exist with Ctx + G. In the same way, E + Nl showed synergism whereas E + G didn't. V + Nl combinations, as active upon Streptococci as V + G, are more active than V + G upon Enterococci. Against Gram negative bacilli, we observed good effects with Cb + Nl. Cephalosporins combinations were also interesting : Cfz + Nl were as active Cfz + G but Czt + Nl showed higher synergistic effect than Cxt + G. Ctx + Nl combinations were effective upon E. coli.