The coordination of the cupric ion to nitrogenous ligands differs in the three compounds: cupric protoporphyrin IX dimethyl ester, cupric benzoyl hydrazone, and cupric ortho-vanillin ethylene diamine. Electron paramagnetic resonance studies have been carried out to yield the spin-hamiltonian and bonding parameters of the cupric ion in these compounds. These parameters are compared with those from related compounds.