Serratia marcescens, Klebsiella sp. and Escherichia coli strains bearing transferable resistance to aminoglycoside antibiotics, namely, gentamicin, tobramycin, kanamycin, streptomycin, lividomycin, and carbenicillin, as well as to a series of more classical drugs, began to emerge in materials from the Frankfurt University Hospital. Plasmids from Serratia, Klebsiella, and E. coli exhibit a broad host range in that they are transferable to E. coli, Proteus mirabilis and Salmonella typhimurium receipients. They are not transferable to Pseudomonas aeruginosa, although in that species plasmids of gentamicin and tobramycin resistance, was well as of resistance to further drugs, were detected in that area as early as in 1973. High-level carbenicillinase has been identified in Serratia and Klebsiella plasmids associated with drug resistance to aminoglycoside antibiotics.