Free indium concentrations can be determined using AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) with no relevant hindrance from the irreversibility of the In3+/In° redox couple at a mercury electrode. The electroactivity, high lability and mobility of the In hydroxy species help in reaching AGNES conditions for a relatively moderate ratio (deposition time):(gain), which decreases with increasing pH due to the growing contribution of the hydroxy species. In the related technique SSCP (Scanned Stripping ChronoPotentiometry), points corresponding to more positive deposition potentials are said to be “at the foot of the wave”. Some of these points can reach equilibrium along the fixed SSCP deposition time, so that these points are effectively AGNES experiments, and free metal ion concentrations (such as those of free indium) can also be computed from them provided sufficiently accurate data are available. A new representation of the SSCP wave allows for the diagnosis of the potential region where AGNES conditions are fulfilled.