The gas-phase kinetics of the reaction of tetrakis(dimethylamido)titanium (Ti(NMe(2))(4)) with NH3 have been measured using a flow tube reactor and FTIR spectrometer. Ti(NM(2))(4) reacts rapidly with NH3 in a transamination reaction to form HNMe(2) as a direct product. The bimolecular rate constant for the reaction of Ti(NMe(2))(4) with NH3 at 24 degrees C is k = (1.2 +/- 0.2) x 10(-16) cm(3) molecules(-1) s(-1). A primary kinetic isotope effect of k(H)/k(D) = 2.6 +/- 0.4 is observed with ND3 indicating that cleavage of an N-H bond is the rate limiting step. Therefore the rate constant is assigned to the initial transamination reaction with NH3. The temperature dependence of the rate constant gives activation parameters of log(A) = -10.0 +/- 0.2 (Delta S dagger = -19 cal/(mol K)) and E(a) = 8.1 +/- 0.1 kcal/mol (Delta H-dagger = 6.9 +/- 0.1 kcal/mol). When excess HNMe(2) is added to the gas flow, the reaction rate is strongly suppressed. This is evidence for a reversible initial transamination reaction : Ti(NMe(2))(4) + NH3 reversible arrow (Me(2)N(3))Ti-NH2 + HNMe(2). The proposed mechanism for subsequent reaction is elimination of HNMe(2) : (Me(2)N)(3)Ti-NH2 --> (Me(2)N)(2)- Ti=NH + HNMe(2). From the dependence of the observed rate constant on HNMe(2), the branching ratio is obtained for the above elimination reaction versus reaction with HNMe(2) : (Me(2)N)(3)Ti-NH2 + HNMe(2) --> Ti(NMe(2))(4) + NH3. The relevance of these results to the chemical vapor deposition of TiN by this chemistry is discussed.