Copper complexes are present in many biological systems dissolved in an isotropic or ordered fluid matrix. For such systems E.P.R. lineshape studies in the slow motion region are often incomplete due to both the slowness of simulation programs and inherent approximations in the fitting routines. The aim of this paper is to describe a fast computational procedure for simulating E.P.R. lineshapes of such magnetic species. We take into account, in a very simple way, the angular dependence of the transition probability. Furthermore we criticize carefully the assumption of deleting, in the slow motion regime, the pseudosecular terms.