Bacillus megaterium GW1, radiolabeled with (DL + meso)-2,6-diamino[G–3H]pimelic acid ([3H]A2pm), was incubated with mixed rumen protozoa, mixed rumen bacteria or alone (control). The protozoa released a large number of radiolabeled compounds into the medium; many of these were peptides. This activity was not found in either rumen bacteria or control incubations. Key words: Protozoa, bacterial cell wall, (DL + meso)-2,6-diaminopimelic acid