A comparative, numerical, taxonomic analysis was carried out on 24 selected strains of Clostridium spp. isolated from cattle slurries and fresh forage grasses fertilized with slurries, as well as on 10 culture-collection Clostridium tyrobutyricum strains for reference. The results showed an unexpectedly low occurrence of the Clostridium tyrobutyricum, with only one of the 24 strains isolated om slurry belonging to this species. The majority of Clostridium strains isolated from grasses were identified as C. malenominatum Although the predominant anaerobic, spore-forming colonizers of the cattle slurry belonged taxonomically to the genus Clostridium they could not be firmly identified, bur appeared to show some resemblance to C. propionicum.