The results of cyclic voltammetric studies on vanadyl mesoporphyrin dimethyl ester, VO(MESO), at various concentration ranges are reported. Redox peaks have been identified for the dimeric species in the cyclic voltammograms. The monomeric radical cation of VO(MESO) has been identified at low temperatures, and the triplet EPR spectrum of this species is reported. The zero-field splitting parameters have been obtained by computer simulation. A distance of 3.8 Angstrom between the d electron in the vanadium orbital and the unpaired pi electron in the porphyrin ring in the monomeric radical cation of VO(MESO) has been obtained, This result is interpreted as arising from a(1u) ground state for the pi electron in the porphyrin.