The mitigation of the heat island effect can be achieved by the use of cool materials that are characterized by high solar reflectance and infrared emittance values. Several types of cool materials have been tested and their optical and thermal properties reveal that these materials can be classified as "cool" with the ability to maintain lower surface temperatures. Cool materials can be used on buildings and other surfaces of the urban environment. Based on these results, a modeling study was undertaken to assess the urban heat island effect over Athens, Greece, a densely populated city, by trying to analyze the impacts of large-scale increases in surface albedo on ambient temperature. Numerical simulations were performed by the "urbanized" version of the nonhydrostatic fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5, version 3-6-1). Two scenarios of modified albedo were studied: a moderate and an extreme increase in albedo scenario. It was found that large-scale increases in albedo could lower ambient air temperatures by 2¡C. Furthermore, the impact of high albedo measures on heat island magnitude was estimated by creating a spatial representation of the urban heat island effect over the modeled area. The results of this study can help to promote the adoption of high albedo measures in building energy codes and urban planning regulations. © 2008 American Meteorological Society.