Streptomycin-resistant enterobacteria were isolated from the faeces of 31 out of 35 patients under streptomycin therapy, in the University Hospital of Alexandria. The isolated bacteria were 26 Escherichia coli, 3 Klebsiella pneumoniae and 2 Enterobacter cloacae. Their resistance patterns have shown that 80% had multiple antibiotic resistance. The MIC of streptomycin for all strains was higher than 312 μg/ml.Nearly 90% of these strains carried resistance plasmids. However, 3 strains possessed no plasmids and were assumed to be mutants. 60% of the plasmid-carrying strains have been able to transfer the resistance by conjugation. The rest have shown small plasmids, some of them were characterized by streptomycin and sulphonamide resistance and a molecular weight of 4.1 mega-daltons