Proton spin-lattice relaxation times of bisphenol-A polycarbonate, butyl rubber, and blends of the two polymers were studied at 18 Mc/sec in the temperature range 90°-450°K. The proton spin-lattice relaxation is primarily dipolar in each polymer, due to methyl group reorientation and to reorientation of chain segments. In a blend of bisphenol-A polycarbonate with 7 and 10 wt of butyl, a nonexponential decay of magnetization was observed in the temperature range 280°-380°K. This was explained by the existence of two spin temperatures in these blends, indicating that processes which bring about the equilibrium within the spin system are slow compared to the spin-lattice relaxation times of the two components of the blend.