A Monte Carlo-probability d. function (pdf) method based on a Lagrangian particle technique to calc. the transported pdf of the thermochem. (scalar) properties was implemented in the finite vol. code KIVA-3 to model three-dimensional premixed transient combustion in a two-stroke engine. The main advantage of the pdf method is that chem. reactions in turbulent flows can be treated exactly, without model assumptions. Turbulent transport is handled by the mixing model of Curl. The pdf model and the computational fluid dynamics (CFD) code are coupled by a hybrid soln. scheme. For each time step, the flowfield is interpolated to match the particle system. The d. calcd. from the thermochem. variables is then returned to the CFD code. The thermochem. system is simplified by a reaction scheme based on the intrinsic low-dimensional manifold (ILDM) method using a table with a few reaction progress variables. The aim of this work is to show that the Monte Carlo technique coupled to an ILDM method can model tech. systems in three spatial dimensions, including the prediction of flame front species such as radicals. The results are compared to measurements of flame propagation using two-dimensional tracer laser-induced fluorescence imaging in an optically accessible two-stroke engine.