We studied the prevalence of liver disease and the carrier state for hepatitis B (HBV), delta virus (HDV) and HIV-1 infection in two Valencian penitentiaries, one for males and the other for females. Serological results were correlated with history of intravenous drug addiction, alcohol abuse, homosexuality or prostitution (high-risk groups), and duration and number of internments. A high prevalence of increased transaminase levels (52.2%) and serological markers for HBV infection (66.5%) was observed amongst the inmates, figures being higher amongst high-risk individuals and inmates confined for more than 6 months. No signs of HDV or HIV-1 infection were found amongst the prison staff. Anti-HIV-1 positivity was observed most frequently amongst individuals combining both drug abuse and homosexuality/and prostitution.