The reaction between BCl3 and NH3 to produce dichloroboramine (Cl2BNH2) and HCl was probed using a flow-tube reactor interfaced to a molecular-beam mass-sampling system. A composite method that couples the detailed simulation of the fluid mechanics and chemical reactions occurring in the flow tube to an algorithm for nonlinear least-squares optimization was used to extract the kinetic parameters from the experiment. The rate constant for this gas-phase reaction is k (cm(3) mol(-1) s(-1)) = 4.21 x 10(11) exp[-(8350 cal mol(-1))/(RT)] with an estimated uncertainty of 10-15% over the temperature range 670-920 K. The results indicate that surface reactions involving BCl3 and NH3 occur in the flow tube, but their contributions to the observed chemical behavior of the system can be quantified and therefore do not affect the kinetic measurements reported here. In addition, the low-energy barrier to this gas-phase reaction has important implications for the chemical vapor deposition of boron nitride from BCl3 and NH3.