A new parametrization for an effective nonlinear Lagrangian density of relativistic mean field (RMF) theory is proposed, which is able to provide a very good description not only for the properties of stable nuclei but also for those far from the valley of beta stability. In addition the recently measured superdeformed minimum in the {sup 194}Hg nucleus is reproduced with high accuracy. {copyright} {ital 1997} {ital The American Physical Society}