We study adsorption-desorption kinetics of polymer chains at a solid surface. Protio polystyrene, adsorbed from cyclohexane to a single surface of oxidized silicon, was displaced by deuterio poly- styrene. A single time constant, ${\mathrm{\ensuremath{\tau}}}_{\mathrm{off}}$, described displacement for a significant time (1--2 h). An aging effect, in which ${\mathrm{\ensuremath{\tau}}}_{\mathrm{off}}$ continued to increase even after mass adsorbed had equilibrated, implied surprisingly slow rearrangements of adsorbed chains in the direction of conformational equilibrium. After equilibration, ${\mathrm{\ensuremath{\tau}}}_{\mathrm{off}}$ increased exponentially with length of adsorbed chains.