The surface acidity of four different anatase preparations has been studied by FT-IR spectroscopy of adsorbed benzene, ammonia, pyridine, carbon monoxide and dioxide. Our results indicate that surface chemistry of anatase, in particular acidity, greatly depends on the preparation of the sample, both through the resulting morphology and the presence of surface impurities. Different morphologies may result in different types of Lewis acid sites. If pure, anatase does not show Brønsted acidity. The presence of silica impurities is responsible for an enhancement of Brønsted acidity on several samples, and may be evaluated by the intensity of an IR band situated near 3730 cm-1. Very strong Brønsted acidity is generated by the presence of sulfate impurities. © 1985.