A search of the computerized database at the National Taiwan University Hospital was made for cefotaxime-resistant and cefmetazole-susceptible isolates of Escherichia coli and Klebsiella pneumoniae (which may be extended-spectrum beta-lactamase-producing strains) in pediatric wards and intensive care units between 1999 and 2001. Fourteen infectious episodes attributed only to study bacteria were identified, including 7 episodes of bacteremia. Nine patients (64.3%) had underlying medical conditions: 3 were premature babies, 3 were immunodeficient, 2 had malignancy, and 2 had a congenital heart disease with active heart failure even after surgery. Among the 7 patients with bacteremias, 5 may be catheter-related; 6 were treated with carbapenems and 1 was treated with cefmetazole successfully, with or without the removal of the catheter. Before the acquisition of the infection, a history of stay in an intensive care unit within 4 weeks was noted in 10 cases (71.4%); a history of use of extended-spectrum cephalosporins within 4 weeks was also noted in 6 cases (42.9%). Cefmetazole, with or without an aminoglycoside, was clinically effective in 6 cases (42.8%). Except for 1 episode of pneumonia that ended in mortality, all of the infectious episodes were successfully treated. The mortality rate was 7.1%.