Eighteen isolates of Bifidobacterium species, 99 of Eubacterium species, and 38 of anaerobic Lactobacillus species were recovered from 3,971 clinical specimens submitted to the anaerobic microbiology laboratory at the National Naval Medical Center over a period of 10 years (June 1978 to June 1988). Clinically significant infection was documented in association with 53 isolates recovered from 52 patients: 8 (44%) of the 18 Bifidobacterium isolates, 30 (30%) of the 99 Eubacterium isolates, and 15 (39%) of the 38 Lactobacillus isolates. The rest of the isolates were considered to be contaminants or to be of uncertain pathogenic significance. The significant infections that were documented mostly involved abdominal abscesses, obstetric and gynecologic sites, and wounds. Predisposing conditions (primarily prior surgery, immunodeficiency, malignancy, presence of a foreign body, or diabetes) were apparent in 7 (87.5%) of the 8 patients infected with Bifidobacterium species, in 23 (85%) of the 27 patients infected with Eubacterium species for whom clinical records were available, and in 8 (67%) of the 12 patients infected with Lactobacillus species for whom clinical records were available. Antimicrobial therapy was administered to 40 (85%) of the 47 patients for whom clinical records were available; such treatment was given in conjunction with surgical drainage or correction for 31 of these 47 patients (66%). No patient died of infection due to anaerobic, nonsporulating, gram-positive rods. These data illustrate that, although Bifidobacterium, Eubacterium, and Lactobacillus species are infrequently associated with infections, they occasionally do cause serious illness.