Statements this week from Public Health England that the UK would soon start mass testing to identify people who have had a Covid-19 infection and recovered, and are therefore immune, have thrown the spotlight on developers of these antibody-based blood tests. Serological tests for antibodies to viruses, such as IgM and IgG, use fairly simple and cheap techniques such as enzyme-linked immunosorbent assay (Elisa). As such they could in theory be produced by many different diagnostics companies and run in almost any microbiology lab in the country. Several small companies have said they are developing these tests – including the US groups Biomerica and Chembio Diagnostic Systems, Germany’s Pharmact and South Korea’s Sugentech. As for UK companies, Surescreen Diagnostics is already selling a Covid-19 test abroad, and an assay for antibodies to the virus plus the inflammatory biomarker C-reactive protein developed by Attomarker is being tested at St Thomas’s Hospital in London. Public Health England has bought 3.5 million serological assays, but has not said from whom. Neither is it clear exactly when the screening programme will begin; the UK government has said that the tests’ accuracy must be ascertained before widespread distribution.