A new model for nematic polymers is proposed, based on the probability psi(u,delu,t) for a macromolecule to be oriented along direction u while embedded in a Vu environment created by its neighbours. The potential of the internal forces is written Phi(u,delu) accordingly. The free energy contains a contribution v(Phi + k(B)TIn psi) where the brackets mean an average over the probability distribution, while v is the (uniform) polymer number density. An equation is derived for the time-evolution of the order parameter S = - I/3, together with an expression for the stress tensor. These two results offer a generalization of the Doi Model in so far as they include a distortional energy, analogue to the Frank elastic energy for low molecular mass nematics. Extending the Maier-Saupe variational procedure, we specify the way that the internal potential Phi(u,delu) must be written for it to favour non-zero values of the order parameter, while giving a penalty to situations with gradients of the order parameter. The result is quite different from the potential proposed a decade ago by Marrucci and Greco (their Phi depends on u only), while it has a clear connection with the so-called Landau-de Gennes (LdG) tensor models, which are based on a free-energy depending on the order parameter and its gradients. (C) 2004 Elsevier B.V. All rights reserved.