The redistribution of a mobile component in a mixed compound A(1+delta)X(v) in a temperature gradient can be studied by means of time-dependent measurments of either the ionic of the electronic thermovoltage. The reduced heat of transport of the mobile componet (Q(A)* or Q(X)*) results directly from the difference of the partial thermovoltages at t --> 0 and t --> infinity : For materials with predominant ionic conductivity, the electronic thermopower hast to be meaured; for materials with predominant electronic conductivity, the ionic thermopower has to be measured. Experimental examples are presented.