Chronoamperometry using a small disk electrode to determine diffusion coefficients was carried out under microgravity conditions, in which convection could not be caused by density heterogeneity in the electrolysis solution. Ferrocene in an acetonitrile solution of 0.1 mol dm(-3) tetraethylammonium perchlorate was used as the test substance. The results obtained under normal gravity were compared with those measured under microgravity. The chronoamperograms measured under normal gravity were not affected by convection for at least 10 s of electrolysis, even in a solution of low viscosity like acetonitrile. The value of the diffusion coefficient of ferrocene in 0.1 mol dm(-3) tetraethylammonium perchlorate-acetonitrile solution at 25 degreesC was (2.53 +/- 0.03) x 10(-9) m(2) s(-1) with an estimated accuracy of 3%. (C) 2003 Elsevier B.V. All rights reserved.