Formalin-fixed, paraffin-embedded cervical tissues from 106 patients which exhibited a colposcopically atypical transformation zone, were examined for the presence of HPV DNA by in situ hybridization using biotin-labeled HPV 6/11 and 16/18 DNA probes. From the comparative study between histologic, cytologic, colposcopic findings and virologic results it is confirmed that HPV 6/11 DNA is detected more frequently in the less severe lesions, whereas HPV 16/18 DNA is predominantly found in the most severe dysplastic lesions.