Whole blood, plasma and relative viscosities and red cell filterability have been investigated in 15 patients with Alopecia areata (A.A.) and in 9, age and sex-matched, normal subjects. Erythrocyte filtration time resulted to be significantly increased in alopecic subjects as compared to the normal subjects. Such parameter also showed a good correlation (r = 0.752) with relative viscosity. Whole blood, plasma and relative viscosities were not significantly different from normal subjects.