We present theoretical calculations of the spin-flip relaxation time of conduction electrons in Cd1-xMnxTe quantum wells. The spin-flip scattering arises from the s-d exchange interaction between the conduction and localized electrons. The scattering efficiency is larger with the localized spins in the well than in the barrier, typical time scales being tens of picoseconds and nanoseconds, respectively. A biased double-quantum-well structure should provide an ideal means for controllable change of the spin-flip scattering time. © 1990 The American Physical Society.