The objectives of our study were to better understand carcinogenesis of gestational trophoblastic tumors and to investigate the possible presence of human papillomavirus types 16 and 18 DNA sequences in these tumors. Amplification-based DNA methodology was used on 11 hydatidiform moles, 5 invasive moles, 8 choriocarcinomas and 9 normal early placental tissues. Human papillomavirus type 16 DNA was not found in any of these tissues. Although human papillomavirus type 18 DNA was also not found in the 9 normal placentas and 5 invasive moles, it was present in 2 of the 11 (18%) hydatidiform moles and in 4 of the 8 (50%) choriocarcinomas.