Computational fluid dynamics (CFD) was used to study some aspects of heat transfer from particles under conditions similar to those found during gas-phase olefin polymerization. The particles considered are initially small (diameter between 10 and 80 mum), thus making it difficult to apply classical heat-transfer correlations. The FLUENT CFD code was used to study the influence of parameters such as the maximum reaction rate, the activation time, particle interaction, and the influence of the initial catalyst particle size on particle growth and thus the production of heat. Results show that, as expected, the larger the initial catalyst particle size, the higher the temperatures inside the particle. Further it is shown that particle interactions play a large role in the heat transfer, especially when studying the effect of the bulk gas flow, both in terms of velocity and direction. It was also demonstrated that because of these interactions, both convection and conduction of heat can be important.