[en] The gyrokinetic particle simulation model is used to study particle diffusion in a toroidal magnetic field. Previous simulations obtained results in agreement with the existing theory for the banana and plateau regimes, but failed to include the charge separation due to the toroidal drifts (the grad B and curvature drifts), which gives rise to the Pfirsch-Schluter diffusion, and which may also play an important role in the banana and plateau regimes. An electrostatic gyrokinetic code including binary collisions which are energy and momentum conserved is developed to study this charge separation effect on neoclassical diffusion. First, the q dependence of the diffusion coefficient is examined without the inclusion of the self-consistent electric field. It is found that the coefficient varies as q² in the banana and plateau regimes, in agreement with the neoclassical theory, and becomes q independent as q gets larger (>5) in the Pfirsch-Schluter regime. Next the charge separation is included by keeping low wavenumber Fourier modes of the electric field in the simulation. Preliminary results show an enhancement of diffusion in the Pfirsch-Schluter regime, and it is found that the dipole moment of the electric potential in the direction of the toroidal drifts is mainly responsible for this enhancement, which agrees with the physical picture of the Pfirsch-Schluter diffusion. These and other results are presented