A simple and rapid procedure is reported for detection of Lacris-Lacbon (Bacillus coagulans) in animal feces by use of immunological specificity. The antiserum against Lacris-Lacbon reacted only with this strain and not with the other 19 strains of Bacillus coagulans. Moreover, the antiserum did not react with any of the 153 strains of acidforming thermophilic bacteria which were isolated from animal feces with modified GYP medium at 55°C. This finding enables us to detect with ease the strain Lacris-Lacbon.