The L1 protein represents more than 90% of the total protein on the surface of the virus. This protein is able to assemble itself, forming virus-like particles (VLPs). VLPs, mainly type 16, have been broadly used for studying the antibody response induced by genital HPVinfection. The VLP-antibody presence is stable in time, correlated with the number of sexual partners, and associated with persistent infection, viral load, and development of neoplasic lesions; this is rarely found in patients suffering from transitory infections. Seropositivity occurs more frequently in patients who have progressed to CIN III and invasive cancer than in those suffering from CIN I or CIN II and the antibody response is significantly higher in women having a higher viral load than those with lower viral load. Prospective studies have shown that 70-90% of HPV-16 infected women are seroconverted between 6 and 18 months after HPV DNA has been detected and that this rarely occurs in patients detected as having transient HPV DNA.