To investigate the metabolism of 18: 2n-6 and 18: 3n-3 by pure cultures of Sharpea azabuensis, two different strains ( RL 1 and ST18) were each incubated in the presence of 40 mu g ml(-1) 18: 2n-6 or 18: 3n-3. Pure cultures of Butyrivibrio fibrisolvens D1 and Butyrivibrio proteoclasticus P18 were included as control treatments. Similar to the metabolism of B. fibrisolvens, both S. azabuensis strains converted 18: 2n-6 or 18: 3n-3 to cis-9, trans-11 CLA or cis-9, trans-11, cis-15 CLnA, after which it was further reduced to trans-11 18: 1 or trans-11, cis-15 18: 2, respectively. B. proteoclasticus additionally reduced trans-11 18: 1 to 18: 0. Trans-11, cis-15 18: 2 was also further metabolized by B. proteoclasticus, although trans-11 18: 1 did not accumulate, and only minor amounts of 18: 0 were formed. The time frame of 18: 2n-6 and 18: 3n-3 biohydrogenation by S. azabuensis was comparable with B. fibrisolvens, indicating that S. azabuensis and B. fibrisolvens might be alternative biohydrogenators of 18: 2n-6 and 18: 3n-3 in the rumen.