Micro heat exchangers may be used for winterisation of biodiesel at temperatures below 273 K. For a proper design of our micro heat exchangers the viscosity of biodiesel must be known around a temperature of 273 K. Therefore, different samples of biodiesel were examined in the range of 258-303 K and empirical equations for the temperature dependent viscosities computed. Above temperatures of 273 K an exponential equation based on the usual Arrhenius form describes all measurements well. Below 273 K the viscosity sharply rises within 2 K and then further increases. The reason is the precipitation of crystalline saturated methyl esters. (C) 2004 Elsevier Ltd. All rights reserved.