The interaction of ultrathin Ti films grown on clean and oxidized W(110) has been studied by Auger electron spectroscopy and thermal desorption. Auger electron spectroscopy indicates layer-by-layer growth of Ti on both of these substrates. For annealing temperatures up to 1100 K, two-monolayer Ti films are stable on the clean and oxidized W surfaces. Above these coverages, the films are unstable after annealing to 1100 K, although this temperature is lower than Ti desorption. Diffusion of oxygen to the Ti surface is also observed for the oxidized surface. Thermal desorption data show distinct Ti monolayer and multilayer features for Ti from the clean surface at coverages greater than one monolayer. A more complex desorption behavior is observed for Ti on the oxidized surface.