To the Editor: We recently encountered proposed studies that explicitly excluded persons in same-sex relationships. We therefore decided to gather data on clinical trials to see whether this phenomenon is common.We performed exploratory searches of the ClinicalTrials.gov database1 to identify categories of studies from which lesbians and gay men were likely to be explicitly excluded. The ClinicalTrials.gov database contains detailed information on more than 80,000 clinical trials sponsored by the National Institutes of Health, other governmental agencies, and private industry. We sought explicit inclusion and exclusion criteria that would restrict trials to heterosexual patients, such as study requirements that . . .