Responding to widespread criticism, the US Food and Drug Administration on May 4 tightened its regulation of tests for antibodies to the SARS-CoV-2 virus. Testing blood serum for antibodies can determine whether a person has been exposed to the virus and recovered from the disease it causes, COVID-19. Such serology tests could provide valuable information about the spread of the disease and whether people are immune to it. But widespread antibody testing for SARS-CoV-2 has been hampered by lack of availability and questions about test accuracy. The FDA issued a policy March 16 that allowed serology tests to be distributed and used if companies validated the tests internally, notified the agency, and included warning statements with the tests that the FDA had not reviewed them. That approach led a congressional committee to conclude in April that “FDA is unable to validate the accuracy of antibody tests that are already on the market, and companies are ignoring requests from the Department of Health and Human Services to voluntarily submit their tests for validation.” The FDA’s updated serology test policy now includes recommendations for specificity and sensitivity and requires companies to submit antibody test validation data to the agency.