Understanding the process of fouling is of utmost importance considering its usually considerable impact on the overall performance of a process plant. Crystallisation fouling is one of the most commonly encountered problems in industry. Despite significant advances made by crystallographers in understanding mechanisms of crystallisation, researchers working in the filed of fouling in heat exchangers have tended to ignore certain basic features of crystallisation. Generally the rate of crystallisation fouling is simply taken as a function of concentration difference occurring in heat exchangers and reaction rate constant. The aim of this study was to analyse crystalline deposits forming on the heat transfer surface and hence determine the effect of particles on crystallisation fouling. It was found that deposit formation pattern changed significantly when particles of the crystallising material were introduced into the process solution. These particles settled on the heat transfer surface and provided new nucleation sites for crystal growth. As a result, many additional crystals were formed and the rate of crystallisation enhanced significantly. In contrast, particulate fouling by these particles was found to be insignificant. Based on these results, it is argued that there is a need to modify the crystallisation fouling models to incorporate the enhancement effects of the particles.