Anaerobiospirillum succiniciproducens is a motile, spiral anaerobic bacterium with bipolar tufts of flagella. Reports of clinical illness due to A. succiniciproducens are rare. In a retrospective review of anaerobic isolates referred to the Centers for Disease Control (CDC) from January 1, 1975, through January 31, 1986, isolates of A. succiniciproducens from the blood of 21 patients were identified. A single patient whose blood isolate had not been received at CDC was included in the review. These 22 patients were from 15 states. Their mean age was 58.6 years. Underlying disorders included alcoholism, atherosclerosis, malignancy, surgery, diabetes mellitus, and dental caries. Clinical features included gastrointestinal tract signs and symptoms in 17 (77%) of 22, fever greater than 38 degrees C in seven (37%) of 19, and leukocytosis of more than 10,000 cells/mm3 in 11 (58%) of 19. Although 16 patients received antimicrobial therapy, its effect on outcome was unclear. A. succiniciproducens was reported to have contributed to the deaths of seven patients. Disorders predisposing patients to anaerobic infections may put them at increased risk for A. succiniciproducens bacteremia. The presence of antecedent gastrointestinal tract signs and symptoms suggests that the gastrointestinal tract might be the primary portal of entry.