We report a convenient, rapid, and reproducible method for the synthesis of stable dispersions of uniform gold nanoparticles at ambient temperatures. The method consists in mixing aqueous solutions of tetrachloroauric acid and iso-ascorbic acid. The influence of the experimental conditions on the size of the gold particles and the stability of the final sols as determined by dynamic light scattering and UV–vis spectrophotometry will be discussed. Since the preparation process does not require the addition of a dispersing agent, the surface of the resulting gold nanoparticles can be easily functionalized to make them suitable for applications in medicine, biology, and catalysis. Their interactions with biomolecules was studied using a model protein.