PAmXD,6 [poly(m-xylylene adipamide)] was processed using a Brabender plastograph at 30 rpm and at 265 +/- 5 degrees C. The evolution of the M(n) versus mixing time determined from solution viscosity and chain end concentrations measurements shows that PAmXD,6 undergoes hydrolysis or condensation reactions depending on its initial molecular mass. Lower masses undergo condensation while higher masses undergo hydrolysis. The determination of water concentration in the melt during mixing time confirmed that this behavior is related to an equilibrium constant which was estimated at 500 +/- 100. For a mixing period shorter than 20 min, a good correspondence was observed between M(n) values determined either by chain end concentrations or by solution viscosity. However, for a mixing period longer than 20 min, discrepancy between M(n) values using both methods witnesses the probable appearance of oxidative degradation of PAmXD,6. Mechanisms adapted from the established oxidation reactions of PA6 and PA6,6 are proposed to justify the PAmXD,6 behavior. Those reactions could explain the slight yellowing of PAmXD,6 during its processing. It was also shown that the PAmXD,6 Brabender plastograph mixing torque (30 rpm, 265 +/- 5 degrees C) is linearly related to M(n) in a log/log diagram.