Cavitation nuclei are added to the flow to achieve adequate scaling of cavitation phenomena in model-scale facilities with respect to full-scale conditions. During propeller cavitation studies in MARIN’s Depressurized Wave Basin (DWB), cavitation nuclei are added to the flow using electrolysis. In the present study, Interferometric Particle Imaging (IPI) was applied to determine the size and the concentration of nuclei in the wake of a ship model. The dependence of the nuclei size and concentration spectra on the electrolysis current and the basin pressure showed good agreement with theory. One limitation of the present technique was identified: the minimum size of nuclei that can be resolved is approximately 40 μm. This also limits the basin pressure at which nuclei measurements can be performed to a maximum of approximately 100 mbar.