A two-times Green’s function formalism is used together with linear response theory to derive general equations, valid at any temperature, for the effective nuclear relaxation times in metals. The results obtained by selecting the smallest-order pole in the Green’s function as the first approximation are in complete correspondence to experimental evidence at high temperatures and exhibit a maximum when the temperature is lowered below the nuclear spin temperature. The results are also compared with those given by Shibata et al. and good agreement is obtained in the supposition of a single-exponential spin-lattice relaxation process.