A simple technique for determining spin-correlated crystal field parameters from spectroscopic data, which depends on the superposition model, is developed. This avoids the need for detailed simultaneous fits to both free-ion and crystal field parameters and provides a practicable method for low-symmetry systems. New sets of parameters have been obtained for the systems Ho³⁺:YPO₄, Er³⁺:YAlO₃ and Nd³⁺:PbMoO₄. Similar results to those from the detailed fitting procedure were obtained for HO³⁺:LaCl₃. The results conform that the rank-six spin-correlated crystal field contributes significantly to lanthanide crystal field splittings. Copyright © 1986The Institute of Physics.