FISP-MRF is a robust method to acquire T1 and T2 maps. The unbalanced gradient in slice-selection direction should reduce the sensitivity of FISP-MRF on off-resonances. This work investigated the dependency of T1 and T2 values on field inhomogeneities in simulations and measurements on phantoms and in vivo by applying different spatial magnetic field offsets. Depending on the sequence implementation, the measured T1 and T2 values were altered in different ways by the off-resonances. Outcomes showed that the actual implementation of the dephasing moment strongly affects the results. Using a constant instead of variable TR further reduced the sensitivity to off-resonances.