With methods of amperometric titrating and spectrophotometric analysis of compounds of iridium (III) and (IV), and method of cathodic polarisation curves the influence of chemical and electrochemical activation of an iridic electrolyte on the mechanism of electrodeposition of iridium on gallium arsenide was studied. It is shown that after oxidative processing of the electrolyte with anodic current on cathodic polarisation curves at current density up to 1-10 mA/сm² an initial plot, displaced to the positive area, appears. Its presence and analytic data testify on the reduction at these current densities of iridium (IV) to iridium (III). There is no such a plot after reduction processing of the iridic electrolyte with cathodic current.