The purpose of this study is to investigate the possibility of using various plastic wastes containing High Density Polyethylene as polymer additives to asphalt concrete. It was investigated that the influence of HDPE-modified binder obtained by various mixing time, mixing temperature and HDPE content on the Marshall Stability, flow and Marshall Quotient (Stability to flow ratio). The binders used in Hot Mix Asphalt (HMA) were prepared by mixing the HDPE in 4-6% and 8% (by the weight of optimum bitumen content) and AC-20 at temperatures of 145-155 and 165 degreesC and 5-15 and 30 min of mixing time. HDPE-modified asphalt concrete results in a considerable increase in the Marshall Stability (strength) value and a Marshall Quotient value (resistance to deformation). Four percent HDPE, 165degreesC of mixing temperature and 30 min of mixing time were determined as optimum conditions for Marshall Stability, flow and Marshall Quotient (MQ). MQ increased 50% compared to control mix. It can be said that waste HDPE-modified bituminous binders provide better resistance against permanent deformations due to their high stability and high Marshall Quotient and it contributes to recirculation of plastic wastes as well as to protection of the environment. (C) 2003 Elsevier B.V. All rights reserved.