A systematic study is performed of the influence of surfactant and temperature on the aspect ratio and monodispersity of Au nanorods, synthesized by a seed-mediated growth technique in water using cetyl-trimethylammonium bromide (CTAB) as surfactant. The changes in aspect ratio with temperature show all "anomalous" behavior, where the aspect ratio first decreases with increasing temperature, reaching a minimum at about 55 degrees C, and after that increases again reaching a maximum at about 80 degrees C. A physical explanation of the observed behavior is proposed. It has also been studied how the CTAB concentration in the cleansing water used in the post-synthesis treatment of the samples affected the stability of the gold suspension. It was found that without the presence of a surfactant such as CTAB in the washing medium, only very few centrifugations can be carried out without considerable loss of product. Characterization of prepared samples was performed with UV-Vis and TEM. (C) 2009 Elsevier Inc. All rights reserved.