Following a seeding growth approach, gold nanoparticles of diameters 5-40 nm were prepared with 10-15% standard deviation in diameter from 3.5 +/- 0.7 nm gold particle seeds. Particle size can be controlled by varying the ratio of seed to metal salt, and thus any size in the range 5-40 mn can be prepared. The method can also be scaled up to produce 10-100 mg of gold nanoparticles.