Samples taken from 101 healthy pregnant women (49 over and 52 under the 20-week gestational period) and 108 healthy nonpregnant women were tested for human papillomavirus (HPV) types. Using 6, 11, 16, and 18 HPV DNA probes, 3-5 x 10(5) exfoliated cells scraped from the cervix were tested by filter in situ hybridization (FISH). Thirty-five of the pregnant women (34.6%) had evidence of the presence of HPV DNA: with 11.8% (12/101) HPV 6; 7.9% (8/101) HPV 11; 8.9% (9/101) HPV 16; and 5.9% (6/101) HPV 18 positivity. HPV DNA was detected in 20.4% (22/108) of the non-pregnant women. Compared with the healthy, nonpregnant group, the higher level of asymptomatic cervical HPV infection was mainly due to the accumulation of HPV 16 and 18 nucleic acids during the gestational period: with detection of HPV 16 in 8/49 cases (16.3%) and of HPV 18 DNA sequences in 4/49 (7.6%) cases. Screening 6-8 weeks after delivery indicated a decline of HPV positivity. Of the 4/12 HPV type 16 positive mothers, only one retained the presence of HPV 16 DNA, whereas neither of the 2/12 type 18 positive women reacted after birth with the type 18 radioactive probe.