In situ, rapid-scan Fourier transform infrared spectroscopy in conjunction with the infrared absorption intensities is used to construct concentration-time profiles for the gaseous products from thermolysis of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-s-triazine (RDX). The general-purpose pyrolysis cell described is capable of attaining rapid heating rates (8-200K s -t) at various gas pressures (0.048-1000 psi, 0.33 KPa-6.8 MPa) and is an attempt to simulate, insofar as possible, combustor conditions. NO2 is the predominant initial gas product from RDX and, along with HCN, from HMX. [NO2] rapidly diminishes with time owing to its participation in secondary reactions. NO is a minor initial product, if it is present at all, but rapidly becomes a major product owing to secondary reactions. Cisand trans-HONO are clearly present initially. The behavior of N20, CH20, CO, CO2, H20, and HNCO is also described. Substantial sublimation of HMX and RDX occurs at low pressure resulting in the dominance of gas-phase decomposition (products derived from N-N bond rupture). Above atmospheric pressure, a crossover occurs from largely gas-phase to largely heterogeneous condensed phase decomposition reactions (products derived from C-N bond rupture). Therefore, condensed phase reactions must be involved along with gas-phase reactions when discussing nitramine decomposition under rocket motor conditions.