D-ribose utilisation was studied in 60 Brachyspira pilosicoli strains and 35 strains of other Brachyspira species, the majority of which were of porcine origin. Utilisation of D-ribose was demonstrated indirectly by measuring the reduction in pH of densely inoculated tryptone-peptone broth supplemented with 7% foetal calf serum and 1% D-ribose. Among B. pilosicoli strains, the mean reduction in pH units was 1.72 (range 0.95-2.28) in broth with D-ribose and 0.27 (range 0.10-0.40) in sugar-free control broth. For Brachyspira strains other than B. pilosicoli, the corresponding reductions in pH units were 0.37 (range 0.12-0.49) and 0.37 (range 0.15-0.58). In conclusion, porcine B. pilosicoli can be differentiated from other porcine Brachyspira species by a test for D-ribose utilisation.