A combined evaluation of the phenotypical properties of five Serpulina type or reference strains and 163 Swedish isolates of spirochactes from pigs and two from birds was made. The porcine isolates were collected from Herds with a History of dysentery or severe diarrhoea and from Herds chosen at random. On the basis of β-Haemolysis, indole production, hippurate Hydrolysis, and α-galactosidase, α-glucosidase and β-glucosidase activity, the isolates could be divided into four main groups, I to IV, with three subgroups in group III. Group I included the type strain for Serpulina hyodysenteriae (1378). Group II was differentiated from group I only by weak β-haemolysis. Group III included the type strain for Serpulina innocens (13256). Group IV included the pathogenic, weakly Haemolytic strain P43. Group IV-spirochaetes were characterised by their ability to Hydrolyse hippurate and by their lack of β-glucosidase activity. Group I and II-spirochaetes were isolated only from dysenteric or diarrhoeic pigs. There was a statistical relationship between pigs with diarrhoea and the isolation of group IV spirochaetes but no relationship with group III spirochaetes.