The basis of the PHE (formerly the Health Protection Agency) Seroepidemiology Programme is a large collection of sera representative of the general population of England, forming a unique and valuable public health resource. The collection is stored and maintained by the Seroepidemiology Unit (SEU) at the Public Health Laboratory (PHL), Manchester. Sera submitted to the SEU are residues of specimens submitted for diagnostic testing. They sample the population range and are anonymised prior to archiving (retaining age, sex, date of collection and source laboratory only). Collection of sera is continuing through collaboration with the PHE Microbiology Services Division (MSD) and some NHS laboratories throughout England, and has occurred annually since 1986. Over 230,000 sera are now stored and catalogued. The collection can be made available for testing to anyone wishing to use it to address issues related to public health policy.