Electron spin resonance (ESR) spectra of 3-ethoxy-2-oxobutyraldehydebis(N,N-dimethylthiosemicarbazonato)-copper(II) copper(II) (CuKTSM2) and copper(II) tetraphenylporphyrin (CuTPP), in paraffin oil at various temperatures, as well as in oriented dimyristoylphosphatidylcholine bilayer membranes, at 25 degrees C, were simulated using the stochastic Liouville equation formalism and a postconvolution method. It has been recognized that because nitrogen hyperfine couplings are nearly isotropic, they can be easily introduced after a simulation that omits ligand nuclear parameters, by convoluting a stick diagram for the nitrogen splitting with the copper spectrum. For the whole range of temperatures studied (from -10 to +120 degrees C for CuTPP and from -60 to +120 degrees C for CuKTSM2), the line shapes of ESR spectra for these square planar copper complexes can be accounted for by motion. The ESR spectra of Cu(II) in oriented bilayers are well reproduced for the magnetic field both perpendicular and parallel to the membrane plane. Spectra, for which the magnetic field is perpendicular to the membrane plane, can be simulated only if an ordering potential is included.