Pregnant women were examined following healthy pregnancies at term. Amniotic fluids were sampled before arteficial rupture of membranes using closed vacutainer system. Blood samples were also taken from the pregnants simultaneously.Endotoxin concentrations of amniotic fluids were tested by the semiquantitative Limulus amebocyte lysate. Both amniotic fluids and blood samples were tested for the presence of DNA of lymphotropic human herpesviruses. The DNA of human papillomaviruses were tested only in the amniotic fluid samples.One-third of the amniotic fluids tested were found to contain measurable amounts of endotoxin. Lymphotropic herpesvirus DNA was deteced in every fourth amniotic fluid sample and in every 8 th blood sample. The prevalence of papillomaviruses was 7 of 96 samples.No significant correlation was found between the presence of endotoxin and viruses in the amniotic fluids. Epstein-Barr virus, human cytomegalovirus and human herpesvirus type 7 were found more frequently in the amniotic fluids than in blood samples (7 to 1). The prevalence of human herpesvirus 6 and 8 was higher in the blood samples than that in the amniotic fluids.The mean weight of the neonates were not impaired significantly by the presence of either viruses or endotoxin. Possible post partum consequences, i.e. partial immunotolerance to viruses is discussed.