The adsorption of Mo from dilute aqueous solutions (10(-3) to 3 x 10(-2) M) is effected on three samples of titania, two are anatase and the third is P25, which is composed of rutile and anatase. The adsorption isotherms at 298, 318, and 338 K are analyzed using a Langmuir linear equation. The isotherms on P25 showed a distinct inflection point that is reproduced by two linear portions, indicating different adsorption regimes. This adsorption behavior is explained as follows: with low amount adsorbed the adsorption is initiated by protonation of the basic hydroxyls on which the negatively charged MoO42-'s are adsorbed, and this is accompanied by an increase in the pH of the impregnating solution. At higher adsorption the coordinatively unsaturated Ti4+ sites participate in the process, leading to a decline in the initial increase in pH. In the case of the two anatase samples the low surface area resulted in poor distribution of adsorption sites; consequently, the distinction between the two modes of adsorption was not entirely clear. The higher adsorption site density in the case of anatase is accompanied by a lower surface coverage, theta, than that for P25. The heat of adsorption, Q, on the three titania samples showed a linear increase with theta, which is represented by the regression equation: -Q = 95.77 theta - 4.25 (R-2 = 0.993).