Relationships between blood pressure and haemorrheological factors were examined in three groups of dogs characterised by different levels of blood pressure. The groups used were sight hounds (high pressure), retrievers (low pressure) and a mixed group with intermediate pressure. The three groups had different levels of haematocrit and blood viscosity at both high and low shear rates, with the sight hounds showing the highest and retrievers showing the lowest levels for each of the parameters. The plasma viscosities did not differ significantly between the groups. Blood pressure and blood viscosity or haematocrit were not correlated within dog groups, but when the dog groups were considered together, significant positive correlations existed between pressure and viscosity and pressure and haematocrit.