This paper deals with the thermo-rheological behaviour at in-service and handling temperatures (i.e. pumping, mixing, compaction, etc.) of bitumens modified by 9 wt% crumb tire rubber. The use of waste tire rubbers as bitumen modifiers can contribute to alleviate pollution problems derived from discarding scrap tires. Thus, the mechanical characteristics and storage stability of crumb tire rubber modified bitumens (CTRMBs) have been studied as a function of rubber particle size. The addition of ground tire rubber to bitumen increases both the linear viscoelastic moduli and viscosity, at high in-service temperatures, and reduces the storage and loss moduli, at low temperatures, resulting in a more flexible binder in this temperature region. As a consequence, a crumb tire rubber modified bitumen displays enhanced mechanical properties, which improves its resistance to both rutting and fatigue cracking. The presence of insoluble non-spherical particles affects the flow behaviour observed at high temperatures. From the experimental results obtained, it may be concluded that the use of rubber particle sizes lower than 0.35 mm and high shear rates during manufacturing operations is highly recommended. Storage stability of CTRMBs decreases with increasing particle size and storage temperature and takes place by the precipitation of the non-dissolved rubber particles. Only the sample containing rubber particles with a mean particle size of 0.29 mm remains stable under the selected storage conditions. (C) 2004 Elsevier Ltd. All rights reserved.