The paper reports Monte Carlo modeling of backscatter returns of a laser beam from ocean water. The Monte Carlo code used for simulations employs the Stokes vector formalism to account for polarization effects at each scattering event, from either water or suspended particles, and at reflection from or transmission through a stochastic sea surface. Scattering from water and suspended matter are considered separately. The Rayleigh-scattering phase function and Mueller matrix are used for modeling scattering from water. Several forms of phase function and Mueller matrices are used to model scattering from the particles. Ensembles of spheres and spheroids with effectively the same size distribution are considered. Mueller matrices and phase functions computed by the T-matrix method for spheroids and Mie theory for spheres are used in the Monte Carlo simulations. The polarization state of the returns are compared for two cases of water containing spherical or spheroidal scattering particles. These are further compared with results derived from experimental data of Voss and Fry for the Mueller matrix of ocean water, which has a form characteristic of nonspherical particles, in combination with the Henyey-Greenstein phase function. ¿ 1999 American Geophysical Union