The thermal degradation of two heterocyclic polyamides, poly(terephthaloyl trans-2,5-dimethylpiperazine) and poly(oxalyl trans-2,5-dimethylpiperazine), is discussed in terms of rates, activation energies and degradation products. These piperazine polyamides are stable in a vacuum up to approximately 420°C, but beyond this temperature essentially total volatilization takes place. From the rates of degradation an activation energy of 64 kcal/mole was calculated for both polymers, but poly(oxalyl trans-2,5-dimethylpiperazine) volatilizes approximately two to three times faster than poly(terephthaloyl trans-2,5-dimethylpiperazine). The addition of trace amounts of sulphuric acid to poly(terephthaloyl trans-2,5-dimethylpiperazine) prior to its pyrolysis reduced the activation energy of degradation to 55 kcal/mole. Mass spectrometric analysis of the volatile degradation products indicates the appearance of large quantities of carbon monoxide and lesser amounts of water, carbon dioxide, hydrocarbons, hydrogen, pyrazines and pyrroles. The character of the rate curves, the nature of the volatile degradation products, and an activation energy of 64 kcal/mole point to a random thermal free radical degradation. In contrast to the behaviour of aliphatic polyamides, the amide linkages in both poly(terephthaloyl trans-2,5-dimethylpiperazine) and poly(oxalyl trans-2,5-dimethylpiperazine) are quite resistant to acid-catalysed hydrolytic breakdown at elevated temperatures.