Colposcopy is standard for diagnosis of cervical cancer precursors, but the development of diathermy loop electrodes for excision of the cervical transformation zone offers a technique for validation. Loop excision of the transformation zone was performed for 47 consecutive women with dysplasia in colposcopically directed biopsies using 20 x 8-mm electrodes. Specimens were marked for orientation and serially sectioned. All pathology material was reviewed. Although 28% of women had disappearance of dysplasia at the biopsy site, only 9% had no dysplasia in the transformation zone. Half of the women with CIN 1 on directed biopsy had high-grade lesions found in loop excision specimens. Significant discrepancies may be found between the results of colposcopically directed biopsy and loop excision.