Self-assembled monolayers (SAMs) were formed on gold colloids in 50% aqueous ethanol in the presence of alkanethiols, HS(CH2) n R, where R represents a series of neutral and acidic functional groups. Chemiadsorption of alkanethiols onto the gold colloids significantly changed the rates of flocculation of the gold dispersions; the magnitudes of these pH-dependent changes were a function of chain length, n, and the terminal functionality, R, in a manner consistent with formation of SAMs on the colloid surface. The reduced rate of dissolution of alkanethiol-treated colloids by wet chemical etchants, transmission electron microscopy, and X-ray photoelectron spectroscopy data further support the formation of SAMs.