A model is described of directional coupled two-phase composite growth in three dimensions using a combined cellular automaton finite difference (CAFD) approach. The modelling strategy and some preliminary results are presented here for the first time. The model incorporates solute diffusion and a simple cellular automaton growth rule containing a pseudo-curvature algorithm. Despite its limitations, the model is able to simulate some of the structural effects that take place during coupled growth. As a demonstration application the model is applied to eutectic growth in the Pb–Sn system and compared to experimental measurements. The scale of predicted microstructures in the model is close to that measured after directional freezing of Pb–Sn eutectic.