We report measurements on the adsorption kinetics of alkanethiolate monolayers onto a microcrystalline gold surface. Our data indicate that the formation of this monolayer is rapid and is described by the Langmuir adsorption isotherm. The concentration dependence of the monolayer formation rate indicates that there exists an equilibrium for the adsorption/desorption process. We determine from these measurements Delta G(ads) = -5.5 kcal/mol for 1-C18H37SH in n-hexane and cyclohexane adsorbing onto gold and Delta G(ads) = -4.4 kcal/mol for 1-C8H17SH in n-hexane adsorbing onto gold.