Colloidal gold is used in molecular recognition and targeting, electronics and nanotechnology. The appearance of the sample is determined by the size and shape of the gold nanoparticles present. Sizes less than 5 nm are yellowish in color, 5 nm to 20 nm tend to be reddish whereas particles greater than 100 nm are bluish in appearance. Size characterization of colloidal gold is of great importance in order to ensure that the particles are homogenous in diameter and that there are no aggregates present in the dispersion. This is popularly done using electron microscopy techniques, however Dynamic Light Scattering is an excellent technique for rapid characterization determining both the size and detecting the presence of aggregates in solution. The technique is also routinely used for sizing of colloidal silver and other metal colloids.