At low temperatures an external pressure of 1 kbar accelerates the high-spin → low-spin relaxation in the [Zn1−xFex(ptz)6](BF4)2, X = 0.1, spin-crossover system by one order of magnitude. This is due to the large difference in volume between the high-spin and low-spin states of 26 Å3/molecule. The relative vertical and horizontal shifts of the potential wells of the two states as a function of pressure are estimated to be 130 cm−1/kbar and 10−3 Å/kbar, respectively.