A form of Ginzburg-Landau theory with non-local correction is derived which is useful in numerical calculation of the spatial variation of the order parameter for superconductors in zero magnetic field. This form of theory is obtained as an extension of the low-temperature modifications of G-L theory developed by Werthamer and others, and is valid over a considerably wider range of values of temperature and order parameter. Boundary conditions at the interface between two metals applicable under rather general conditions are obtained, and the numerical calculation of the one-electron eigenstates in the presence of a spatially varying order parameter is discussed briefly in an appendix.