Apomorphine acts as contractile muscular agent through an extra cellular calcium mechanism dependent. This activity is accompanied with autoxidacion process producing o-quinone derivates. o-Quinone is also obtained by apomorphine oxidation in acid medium; in basic conditions a hydroxi-p-quinone is formed. In order to characterize the apomorphine derivates species generated via metabolism or chemical mechanism, specially free radical forms, electrochemical and Electronic Spin Resonance studies were done to o and p-quinones metabolites in presence or absence of Calcium ions. The electrochemical study of these compounds using cyclic voltametric indicated that the reduction mechanism consists of two steps, the formation of semiquinonic radical and finally the production of hydroquinone derivatives. Calcium ions not modified the reduction couples of these compounds. Electronic Spin Resonance spectroscopy was used to characterize the radical species generated. The hyperfine constants obtained by theoretical calculations were in agreement with the experimental values. Beside, the radical species generated through apomorphine oxidation were detected using Spin Trapping technique. Finally, these results would be indicating the possible existence of radicals species in the reduction mechanism of o and p-quinone as well oxidation process of apomorphine which could be involved in the contractile activity mechanism.