The pathophysiological significance of hyperviscosity and capillary rarefaction in untreated essential hypertension is unknown. Fifty untreated hypertensive men with capillary rarefaction (intravital capillaroscopy) and 20 age- and sex-matched normotensive controls underwent full haemorheological profiling (blood viscosity at high and low shear, haematocrit, platelet and leukocyte counts, fibrinogen and total protein concentrations, P-selectin levels, erythrocyte and leukocyte filterability rates and erythrocyte deformability and aggregation indexes). Subjects with skin capillary density below the group median had younger age, higher diastolic pressure, higher blood viscosity at low shear, higher P-selectin levels, higher erythrocyte and leukocyte filterability rates, and higher erythrocyte aggregation indexes (all P < 0.01). In contrast, patients with greater skin capillary density had a greater plasma viscosity (P < 0.05). The conclusions were that in untreated hypertensive men, capillary rarefaction and hyperviscosity are associated to an increased diastolic blood pressure and to an adverse haemorheological profile.