Anaerobiospirillum spp., motile, spiral anaerobic bacteria, have been implicated as a cause of diarrhea and bacteremia in humans. Anaerobiospirillumlike organisms and Anaerobiospirillum succiniciproducens were reported from 17 cases of diarrhea. Sixteen of the patients did not have any underlying disorders and recovered from the infection; the other one, who had a heart defect, did not. The formulation of a selective medium for Anaerobiospirillum spp. has enabled a survey of human, cat, and dog feces as possible sources for these anaerobic bacteria. Anaerobiospirillum spp. were not isolated from 527 "normal" human feces but were found in both cat and dog feces. We also describe biochemical tests and API ZYM results ofA. succiniciproducens and anaerobiospirillumlike organisms.