In Kaluza's five-dimensional unified field theory the restriction for the 55 component of the metric tensor γ55=1 demands that the 15 equations for the unified field be weakened. Equations which have been proposed have identically vanishing trace. The equations then admit only a radiation field as source of the gravitational field. By relaxing the condition, this limitation is avoided, while retaining the striking successes of the five-dimensional approach. A scalar function, determined by the 15th field equation apart from integration constants, (...) provides source terms for both the gravitational and electromagnetic fields, in the latter case of polarization type. (shrink)