The reduction of copper(I)-diisopropyldithiophosphate [dialkyldithiophosphate (DDP), alkyl = isopropyl] in an ethanolic medium gives rise to well defined polarographic waves. In the differential mode the polarographic wave divides when the concentration of Cu^lDDP (alkyl = isopropyl) is between 0.3 and 0.4 mM. Limiting current data obtained in the d.c. polarographic mode suggest that the oxidation state of the copper species undergoing reduction is common before and after the division occurs and ESR studies confirm that it is a copper(II) species that is present in solution. Stationary electrode voltammetric observations show that the electrode process occurring is electrochemically irreversible and diffusion controlled. In addition, at long delay times (>60 s), an adsorbed species manifests itself and this can be attributed to the adsorption of a mercury(II)-DDP complex formed from the interaction of mercury metal with the dialkyldithiophosphate ligand.From an analytical standpoint, the differential polarographic currents are linearly related to the Cu^lDDP (alkyl = isopropyl) concentration between 0.07 and 1.0 mM with an inflection to higher slope occurring at 0.4 mM.