Titanium is known as a biocompatible metal characterized by biological and corrosion immunity and good mechanical properties, including a high fracture toughness. In a variety of environments, this metal undergoes "natural" oxidation which determine its resistance to corrosion. It can also be exposed to chemical treatments in acidic or alkaline solutions which "enforces" chemical and morphological changes of Ti surface. Those methods, if well controlled, may increase the effective Ti surface area, making it more biocompatible. However, the morphological and chemical factors responsible for their interactions with biological cells are still not well known. The aim of this work was to compare surface chemical and morphological changes introduced by commonly used aqueous NaOH pretreatment with those occurring in a new "piranha" acidic solution. Particular attention was paid to possible changes which may be decisive for the biocompatibility of the Ti-elements subjected to these surface modifications. Surface analytical techniques such as Auger electron spectroscopy (AES) or X-ray photoelectron spectroscopy (XPS) combined with Ar+ ion sputtering allowed us to investigate in detail the chemical composition of Ti oxide layers. SEM examinations provided morphological characterization of the surface of Ti samples. The results revealed large difference in morphology of Ti surfaces pretreated with different procedures whereas only minor difference in the chemistry of the surfaces were detected. (c) 2007 Elsevier B.V. All rights reserved.