The composition of titanium nitride films prepared by ion beam assisted deposition was studied as a function of the partial pressure of N2 gas in the deposition volume, and as a function of the impingement 'ratio of nitrogen ions (500 eV) to evaporated titanium atoms. The amount of nitrogen incorporated from the ambient gas was derived by subtraction of the fraction introduced by the ion beam. It is shown that the primary effects of ion bombardment are an increase in the sticking coefficient and a reduction in the number of active surface adsorption sites.