The high quantum yield and exclusively photo-stable excitation of gold nanoparticles combined with their bio-inert characteristics make them ideal cellular markers. The aim of the study was to visualise gold nanoparticles size-dependently as colloid and in cells after co-incubation. We show the quantification of colloidal gold particles by standard confocal microscopy down to the single particle level. A calibration is demonstrated for pixel numbers in dilution series of uncoated gold nanoparticles. We give implications for practical use of advanced cellular imaging in cultured cells.