Accelerated ageing at 100degreesC of mixtures of RHA (RDX + 6% HMX) and lead has demonstrated that these components are incompatible. The rate of reaction to give N2O, hexamine and triazine was shown to be dependent upon the particle size of the lead, and pressing pressure for discs of these mixtures. In some cases there was more hexamine than RDX after 320 h at 100degreesC. It is suggested that the preparation of the sample for the standard vacuum stability test (compatibility test) should be modified, using particles of explosive and nonexplosive of comparable size, and possibly even pressing, in order to simulate the conditions present in operating systems.