A very general method to determine directly the one-body density matrix which minimizes the total energy of a nuclear system in the Hartree-Fock approximation is proposed. The approach corresponds to a multiparameter search which leads to a system of nonlinear equations. A suitable linearization generates a simple iterative procedure which converges in few steps. The method is applied to find energy and wave function of the4He ground state by using the Brink-Boeker effective nuclear interaction. The results appear to be very good also when the starting density matrix is quite away from the solution. A comparison is made with other approaches to the solution of the HF problem.