This study focuses on the importance of solute dissolution kinetics for cloud droplet formation. To comprehensively account for the kinetics, a numerical model of the process was developed. Simulations of cloud droplet growth were performed for solute diffusivity, droplet growth rates, dry particle and droplet diameters relevant for ambient conditions. Simulations suggest that high ambient supersaturations and low solute diffusivity are major contributors to significant decreases in effective solute surface concentrations during droplet growth. The numerical simulations were incorporated into Köhler theory to assess the impact of dissolution kinetics on the droplet equilibrium vapor pressure. The modified Köhler theory implies that only CCN with slowly dissolving solute could have a "dynamical" equilibrium saturation ratio that is appreciably different from that obtained using thermodynamic equilibrium arguments alone. Copyright 2007 by the American Geophysical Union.