Particulate matter (PM) collected from mainstream tobacco smoke is a test article commonly used for in vitro genotoxicity and cytotoxicity testing of combustible tobacco products. However, little published data exists concerning the stability of PM. We completed a 2year study to quantify the effect of PM storage at −80°C, on the genotoxicity and cytotoxicity of PM generated from 3R4F and M4A reference cigarettes. The Ames test, Micronucleus assay (MNvit), Mouse Lymphoma assay (MLA) and the Neutral Red Uptake assay (NRU) were used. The majority of M4A and 3R4F PMs were genotoxic and cytotoxic at the timepoints tested. Some minor but statistically significant differences were observed for stored versus freshly prepared PM, but the magnitude of changes were within the variability observed for repeat testing.