The optimisation of batch ultrafiltration for product recovery is analysed. Assuming limiting flux operation and rejection coefficients of one and zero for the macrosolute and microsolute respectively, an expression is derived for the total profit of the process where that profit is defined as the value of the recovered microsolute minus the operating cost. It is found that in order to maximise the profit, the ultrafiltration should be stopped when the macrosolute has reached a concentration c(lim)/e(alpha) where c(lim), is the so-called limiting concentration of the macrosolute and alpha is a dimensionless number that represents the ratio of operating costs to product value. No optimum exists when the system is operated at constant flux. (C) 2014 Elsevier Ltd. All rights reserved.