The concept of “flux” is proposed for quantitatively describing the manner in which the relative concentrations of three chain ends remain at a steady state in a terpolymerization. The flux is a measure of the net rate of transition from one chain end to another. If a terpolymerization remains at a steady state with respect to the relative concentrations of the three chain ends, then the flux must be either zero or some finite number which is independent of the choice of chain ends used to calculate it. It is a necessary and sufficient condition for Ham's concept of sequence reversibility to be true that the flux be zero. The flux calculated for many systems using reactivity ratio data is quite near zero. However, the calculations necessarily share the imprecision of reactivity ratio data. Ter-polymer sequence distribution data, if available, could be used in a proposed method of calculating flux.