A theory of nuclear forces is developed, based on the hypothesis that the interaction between a nuclear particle and the mesotron field is strong. Two types of mesotron fields are considered, the charged scalar and the neutral pseudoscalar. The latter, for large enough separation, gives forces between two nuclear particles of the same type as those obtained from perturbation theory and, hence, with the spin dependence and exchange properties required to fit experiment. However, at closer approach the forces become ordinary (non-spin-dependent). It is found impossible to obtain spin dependent forces which, at the same time, extend to small separations and are of sufficient strength to account for the properties of the deuteron.