For a Co complex in an optical transmission experiment and for a Fe co
mplex by means of a dilatometer, the spin crossover between a paramagn
etic high-spin state and a diamagnetic low-spin state has been observe
d to shift to the paramagnetic side in magnetic fields up to 20 T. In
a thermodynamic analysis, the quadratic dependence of the shift in the
spin transition can be evaluated quantitatively.