In a double-blind randomized trial, imipenem/cilastatin (I/C; 500 mg every 6 hours) and ampicillin/sulbactam (A/S; 3 g every 6 hours) were compared in regard to their efficacy for initial empirical and definitive parenteral treatment of limb-threatening pedal infection in diabetic patients. The major endpoints of treatment were cure (resolution of soft-tissue infection), failure (inadequate improvement, necessitating a change in antibiotic therapy), and eradication (clearance of all pathogens from the wound and any bone cultures). Patients in the two treatment groups were similar in regard to the severity of diabetes; presence of neuropathy and peripheral vascular disease; site and severity of infection; pathogen isolated; and frequency of osteomyelitis (associated with 68% of the 48 A/S-treated infections and 56% of the 48 I/C-treated infections). After 5 days of empirical treatment, improvement was noted in 94% of the A/S and 98% of the I/C recipients. At the end of definitive treatment (days' duration [mean +/- SD]: 13 +/- 6.5 [A/S], 14.8 +/- 8.6 [I/C]), outcomes were similar: cure, 81% (A/S) vs. 85% (I/C); failure, 17% (A/S) vs. 13% (I/C); and eradication, 67% (A/S) vs. 75% (I/C). Treatment failures were associated with the presence of antibiotic-resistant pathogens and possible nosocomial acquisition of infections. The number of adverse events among patients in the two treatment groups was similar: 7 in the A/S group (4 had diarrhea and 3 had rash) and 9 in the I/C group (5 had diarrhea, 2 had severe nausea, 1 had rash, and 1 had seizure). Efficacy of A/S and I/C is similar for initial empirical and definitive treatment of limb-threatening pedal infection in patients with diabetes.