A study of human papilloma virus (HPV) specific cellular and humoral immunity in 30 patients with genital warts is reported. By in vivo testing with purified, inactivated plantar wart virus, a cell-mediated immunity to HPV was determined in 60% of patients. Circulating antibodies, evaluated by immunofluorescence testing, were rare, but these increased after an intradermal test had been carried out, especially in patients with a positive skin test, suggesting a booster effect. No significant difference was found between this group of patients and those having skin warts. Our results showed a specific immune response to HPV in most patients, confirming the role of the viral agent in the induction of genital warts.