Human cervical cancers are often associated with human papillomavirus (HPV). In HPV-positive cervical cancers, the oncoproteins E6 and E7 are consistently expressed. In this study, the effects of antisense inhibition of both proteins were examined. Phosphorothioate oligonucleotides (ODNs) AE6 and AE7 complementary to regions flanking the start codons of HPV16 E6 and E7 genes, respectively, were synthesized. These anti-HPV ODNs inhibited the growth of cervical cell lines CaSki and SiHa, which harbor HPV16 but had little effect on cells that do not. Both ODNs also affected the ability of CaSki cells to form colonies in soft agar. In nude mice, treatment with either AE6, AE7, or a mixture of both led to substantially smaller tumors. AE7 was observed to inhibit E7 synthesis. The AE6 ODN probably exerts its effect by suppressing the expression of E6 as well as E7. Cell cultures and tumors treated with AE6 showed a decrease in E7 expression. In addition, an antisense ODN targeted at the retinoblastoma gene was able to reverse some of the inhibitory effect of AE6 on CaSki cells, indicating that AE6 inhibited E7 synthesis. This study further demonstrates that anti-HPV ODNs may be useful therapeutically.