The influence of segregation on the yield of the series-parallel reaction system A + B --> R, B + R --> S is studied. The reactants A and B are initially assumed to be in a periodic array of alternating lamellae and the reaction and diffusion processes are then followed by numerical simulation. We find that the ultimate yield of R can be significantly reduced when compared with the well-mixed case, if the scale of segregation is large. By comparison with the well-mixed case, it is possible to correlate the ultimate yield of R as a function of a Damkohler number based on both reaction rate constants and the lamellar width. This correlation is a weak function of the ratio of the rate constants and the relative amounts of A and B present at the start of the reaction.