The UK government has carried out a research programme studying military capability under conditions of chemical warfare at a facility at Porton Down, Wiltshire, since World War I. In 2001 the Ministry of Defence commissioned a cohort study to investigate the long-term health effects on military veterans of their participation in this programme. We assessed the availability and quality of exposure assessment data held in the archive at Porton Down for the purpose of this study. This involved looking in detail at exposure data in a sample of 150 veterans and undertaking a general review of all available records held in the archive. These sources suggested that the Porton Down records were largely complete and included sufficient identifying information for linkage with service personnel data and with national mortality and cancer registration records. Servicemen usually had multiple tests so data were most readily available in a test-wise format, allowing subsequent aggregation of tests by individual. The name of the chemical used in each test could be determined for most tests and most of the named chemicals could be categorized into major groups for epidemiological analyses. For the major groups (vesicants and nerve agents), quantitative data were available on exposure and on acute toxicity. Standardization will be required of the several different units which were used. Based on this study, exposure assessment for the cohort study of Porton Down veterans will involve abstraction of the name of the chemical used in each test, with quantitative data on exposure and acute toxicity for vesicants and nerve agents. Our results here show that experimental records at Porton Down offer a unique and valuable resource for reconstructing the chemical exposures used in this research programme. The resulting cohort study has the potential to provide information which will assist in understanding the long-term health impact of chemical warfare agent exposure on these veterans.