It has previously been demonstrated that the rigid limit spin Hamiltonian parameters of a non-blue (Type II) square-planar copper complex can be determined in a low viscosity fluid at room temperature by a suitable combination of multifrequency EPR (spectra obtained from 1 to 35 GHz) and computer simulation. It has been shown that these parameters, which permit in combination with molecular orbital theory a description of the electronic structure of the complex, are not the same in fluid phase as in frozen solution, and this is significant in understanding the structure of biologically active copper complexes. This previous approach using motional narrowing theory will be extended to the slow tumbling domain using a "full treatment" computer program wirtten by G. Moro according to the Freed development of the stochastic Liouville equation. Spin Hamiltonian parameters can then be determined for larger molecular weight complexes and for complexes in more viscous environments; the temperature dependence of these "effective rigid limit" parameters will be studied. This methodology will be used to characterize copper complexes of catechol derivatives, histidine, and several antitumor agents, namely bis- and mono-thiosemicarbazones, bleomycin, and adducts of these compounds with biologically available Lewis bases. The new multifrequency EPR methodology will permit obtaining information from these copper complexes in a cellular environment. Experiments will be carried out on Ehrlich cells and red blood cells. The approach will be extended to Blue Type I copper complexes.