Micro-mixing calculations based upon a simplified non-deforming one-dimensional diffusion-reaction formulation are presented for the sequence of three reactions denoted by A + B --> R + B --> S + B --> T. This tripler reaction under micro-mixing is posed as five simultaneous parabolic partial differential equations which have been solved using a general purpose NAG library algorithm. The primary product R has an improved yield under perfect mixing conditions. The ultimate product T is shown to be always favoured by the perfect segregation of micro-mixing. By contrast, the central intermediate S gives high yields under micro-mixing at low conversions, but perfect mixing is preferable at higher conversions. in addition, predictions show that yield improvements for S might be possible by an engineered stretching of fluid lamellae and by the combination of micro-mixing followed by perfect mixing, especially at intermediate levels of conversion. The calculations are relevant to multi-step halogenations and they help to explain how the anomolous appearance of a tri-halogenated species ahead of mono- and di-halogenated ones in a stirred vessel can be attributed to micro-mixing.