Polymerase chain reaction (PCR) procedures for Ruminococcus spp. were developed and used for the detection of Ruminococcus spp. in human and animal faeces. The PCR specificity was established for Ruminococcus albus, R. bromii, R. obeum, R. callidus and R. flavefaciens. The PCR sensitivity ranged from 4 to 100 cells of the pure cultures, depending on the species. Ruminococcus albus, R. bromii, R. obeum and R. callidus were detected in human faeces. R. bromii, R. albus and R. obeum were also detected in animal faeces. R. flavefaciens was not detected in most of the samples tested, except for a weak positive in monkey faecal specimens. The PCR appears to be a specific and efficient method for the detection of Ruminococcus spp. in faecal specimens.