Vaginal swabs were collected monthly from 100 asymptomatic Thai pregnant women as well as from 11 pregnant women with herpetic lesions of the vulva for isolations of HVH, mycoplasma and gonorrhoea. In asymptomatic mothers, 25% and 21% of cases were positive for HVH and mycoplasma respectively. Mixed infections of HVH and mycoplasma, and HVH and gonorrhoea were also found in 27% and 1% of cases respectively. Follow-up in asymptomatic pregnant women and those with herpetic lesions showed positive HVH fluctuations throughout the course of study. Positive HVH was recovered from 48% of amniotic fluid and 32% of breast milk of asymptomatic pregnant women with positive HVH genital isolates, and in 72.7% of aminotic fluid and 36.4% of breast milk in patients with herpetic lesions. HVH was also isolated from 84% of infants of asymptomatic mothers positive for HVH, and 100% of patients with herpetic ulcer. HVH was isolated most frequently from the throat and also from nose, eyes, and ears but with less frequency. IgM antibodies were found in three infants born of asymptomatic mother and in one infant of a mother with herpetic lesion. The low percentage of IgM antibody was interpreted to mean that the HVH isolated from the newborn infants were acquired during passage through the birth canal.