A multiple trauma patient failed treatment with ceftazidime and amikacin for bacteremia and meningitis due to a Kiebsiella pneumoniae strain that produced a novel, plasmid-mediated ,B-lactamase. Both pre-and posttreatment isolates were resistant to ceftazidime (MIC, 264 ,Lg/ml) and various penicillins but not to other expanded-spectrum cephalosporins. The j-lactamase had a pl of 5.25 and was encoded on a conjugal plasmid of approximately 150 kilobases. DNA hybridization studies indicated that the enzyme was a TEM derivative.