Leuconostoc species, a gram-positive coccal bacterium that is classically moderately susceptible to ampicillin and penicillin and resistant to vancomycin is a potential pathogen in the immunocompromised host. Twenty-eight isolates were collected from patients' blood culture specimens in the year 1989-1990. The clinical history and course of nineteen of these patients were studied. Five of them recovered without any antimicrobial therapy and in eight patients Leuconostoc species was isolated with other organisms in the blood culture specimens. The question arises as to when Leuconostoc species is of clinical significance when isolated in the blood culture specimens of patients.