We present a robust method to retrieve neuronal fibers in human brain w hite matter from High-Angular Resolution MRI (HARDI datasets). Contrary to class ical fiber-tracking techniques done on the traditional 2nd-order tensor model (D TI) which may lead to truncated or biased estimated diffusion directions in case of fiber crossing configurations, we propose here a more complex approach based on a variational estimation of Orientation Diffusion Functions (ODF) modeled wi th spherical harmonics. This kind of model can correctly retrieve multiple fiber directions corresponding to underlying intra-voxel fibers populations. Our tech nique is able to consider the Rician noise model of the MRI acquisition in order to better estimate the white matter fiber tracks. Results on both synthetic and real human brain white matter HARDI datasets illustrate the effectiveness of th e proposed approach.