Differential diffusion coefficients of cobalt chloride in water at 298.15 K, and at concentrations from 8 x 10(-3) mol dm(-3) to 3 x 10(-1) mol dm(-3), have been measured using a conductometric cell and an automatic apparatus to follow diffusion. The cell uses an open ended capillary method and a conductometric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times. The results are discussed on the basis of the Onsager-Fuoss and Gordon models.