Totally 70 Escherichia coli (E. coli) isolated strains from patients in Chang Gung Memorial Hospital, Kaohsiung Medical College affiliated Chung Ho Memorial Hospital and the Navy General Hospital of the Republic of China, all in Kaohsiung, were collected during the period of July 1986-August 1987 and examined for their susceptibility to several antimicrobial agents as well as for their plasmid contents. The isolates tested showed a high level of resistance to ampicillin (Ap) (90.4%), piperacillin (Pip) (89.0%), tetracycline (Tc) (88.7%), streptomycin (Sm) (87.7%), chloramphenicol (Cm) (78.4%), kanamycin (Km) (72.6%) and sulfamethoxazole/trimethoprim (Sxt) (54.2%). Observations of the resistance patterns revealed that the dominant type was Ap-Tc-Cm-Sm-Pip-Km. The results of plasmid curing and transfer experiments indicated that three plasmids with molecular weights 49.2-51.6 Mdal, 69.8-178 Mdal and a third one with molecular weight larger than 178 Mdal carried resistance determinants for Gm-Nn, Sm-Km-Tc and Tc-Cm-Km, respectively.