The synthesis and characterization of water-soluble dispersions of gold nanoparticles by the reduction of a potassium tetrabromoaurate precursor solution using the amino acids L-tyrosine, glycyl-L-tyrosine, and L-arginine using alkaline synthesis conditions are reported. The particle sizes determined by small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) measurements are found to be inversely proportional to the rate of particle formation, which was determined by time-resolved UV-visible spectrophotometry measurements, and vary very slowly at intermediate gold concentrations and rapidly at the extremes. Dispersions produced with a mixture of the two amino acids glycyl-L-tyrosine and L-tyrosine showed particle sizes and particle size distributions which were directly proportional to the ratio of the two L-amino acids, thus offering the possibility for control over the properties of the gold nanoparticle dispersions.