A theoretical model is described for coulometry employing a flow electrolytic cell with a porous electrode working under condition of a limiting current. The model allows the “cell factor” of a flow electrolytic cell to be calculated. The possibility of eliminating secondary electrochemical reactions in the flow coulometric determination is discussed. A relation is derived for the upper limit of the chemical rate constant in an e.c.e. mechanism, so that the second electron transfer will not be observed in the flow coulometric determination.