Clostridium butyricum MIYAIRI 588 (CBM 588) is a nonpathogenic, anaerobic, gram-pos. bacillus characterized by the production of short-chain fatty acids, including butyrate. The safety and tolerance of CBM 588 was investigated as a feed additive for broiler chickens, weaned piglets, and turkeys. CBM 588 administered to broilers at doses up to 5 × 107 CFU/g feed for 42 days produced no detrimental effects on zootech. performance, natural mortality, hematol., or biochem. parameters. Piglets receiving CBM 588 at doses up to 5 × 107 CFU/g feed for 42 days showed no significant differences from controls in zootech. performance, mortality, or morbidity. Finally, CBM 588 administered to turkeys at doses up to 2.5 × 107 CFU/g feed for 84 days produced no detrimental effects on zootech. performance, hematol., or biochem. parameters. Some improvements in zootech. performance were seen with CBM 588, including improved average daily gain (ADG) and feed conversion for broilers from days 1 to 21 as well as final body weight and overall ADG for turkeys. Overall, CBM 588 administered in feed at dose up to 5 × 107 CFU/g (broilers and piglets) or 2.5 × 107 CFU/g (turkeys) was shown to be safe and well-tolerated in all tested animals and may provide some nutritional benefit when added to standard com. feed.