New therapies for vancomycin-resistant Enterococcus faecium (VREF) infections are urgently needed. We describe the treatment of 15 patients with VREF infection with quinupristin/dalfopristin (RP 59500), a new injectable streptogramin antibiotic. Primary infections treated were bacteremia (4), urinary tract (4), intraabdominal (5), otitis externa (1), and meningitis (1). Minimum inhibitory concentrations for quinupristin/dalfopristin ranged from 0.5 microgram/ml or less to 2 micrograms/ml, and minimum bactericidal concentrations were greater than 64 micrograms/ml for all VREF isolates tested. Peak serum inhibitory titers following infusion of quinupristin/dalfopristin ranged from 1:8 to 1:64; all bactericidal titers were less than 1:2. Development of resistance to quinupristin/dalfopristin during therapy was not observed. The only drug-related adverse effect noted was phlebitis in 4 patients; all had received quinupristin/dalfopristin by peripheral venous infusion. Three patients had clinical and bacteriologic cures. Relapses occurred in 5 patients with recovery of VREF from infected sites in post-treatment cultures. Ten patients died of severe underlying disease; VREF was believed to contribute directly to the death of only 1 patient. While evaluation of clinical efficacy was complicated by the severity of underlying disease in patients with VREF infection, our experience suggests that quinupristin/dalfopristin is a safe and potentially useful agent for the treatment of VREF infections.