Variation in the nucleotide sequence of the HPV 16 E7 gene in preinvasive cervical intraepitherial neoplasia (CIN) and invasive cervical carcinoma specimens was analyzed. Direct DNA sequencing of PCR-amplified products with primers different from those used for PCR with 5'-end labeling generated distinct sequence ladders with a low background, even in specimens containing relatively low copy numbers of HPV. Of 14 cervical neoplasias, 11 cases showed sequence diversity from prototype HPV16, and a total of 22 nucleotide exchanges were detected. Nine of these led to single amino acid exchanges: [Thr5] to [Lys5] in one case and [Asn29] to [Ser29] in eight cases. The [Ser29] E7 was distributed uniformly among invasive carcinomas and precancerous legions, and was also found in a normal cervix. The [Lys5] E7 and [Ser29] E7 had transforming potential similar to the prototype E7 assessed by cooperation with the activated ras gene in rat embryo fibroblasts.