SummaryModerate resistance to ceftazidime (MIC 4–8mg/l) was detected in strains ofKlebsiella pneumoniaeand Escherichia coliisolated from several patients in the intensive care unit. Moreover, from one of these patients which was treated with ceftazidime, an isolate ofK. pneumoniaethat displayed high-level resistance to this antibiotic (MIC 256 mg/l) was subsequently isolated. Both the low-level and high-level resistance to ceftazidime were self-transmissible to a sensitive strain ofE. coliK 12. Resistance to gentamicin, tobramycin, tetracycline, sulfonamide and trimethoprim was co-transferred in all cases. The activity of the B-lactam antibiotics was significantly enhanced by combination with clavulanic acid.