Four anaerobic strains were isolated from the rumen of the cattle which showed no specific toxic symptoms when fed Leucaena.HPLC anal. confirmed that all of these strains (BR-1, BR-2, BR-5 and BR-7) possessed degradative activities toward the Leucaena toxins mimosine, 3-hydroxy-4 (1H)-pyridone (3,4-DHP) and 2,3-dihydroxypyridine (2,3DHP).In vitro pure and mixed cultures of these four strains degraded 44-59% of mimosine, 30-47% of 3,4 DHP, and 58-60% of 2,3 DHP in 3 days.Strains BR-1 and BR-2 were almost identical and were characterized as Lactobacillus; they may represent a new species.Strains BR-5 and BR-7 were characterized as Streptococcus bovis and Clostridium sporogenes, resp.This is the 1st report that these Gram-pos. facultative, obligate anaerobic bacteria are able to degrade mimosine, 3,4-DHP and 2,3-DHP.These detoxifying bacteria existing in the rumen microflora of cattle in Weizhou island protect therefore their hosts from Leucaena toxicity.