Most investigators concur that infection with certain types of human papilloma virus (HPV) place a woman at high risk for cervical neoplasia. Testing may help identify patients at higher risk. Infection with multiple types of genital HPV is common, however, so prevalence of HPV in women with normal Pap smears is high. This limits the value of screening for HPV. In women with atypical squamous cells of undetermined significance (ASCUS) on Pap smear, finding certain high-risk types of HPV increases the likelihood that the cellular abnormality represents a squamous intraepithelial lesion rather than a benign reactive process. Also, women with ASCUS and a low-risk HPV type usually have lesions that do not progress. Since there are both false-negative and false-positive results, the NCI Workshop recommends the use of HPV testing "only by physicians who understand its limitations" (O'Leary).