The C100-3 antibodies to HCV can be examined with a Chiron kit but only the antibody to non-structure-4 can be. The antibodies in sera of pregnant women were examined by a passive hemagglutination method (PHA), which is one of the second generation kits used in detecting antibodies to the hepatitis C virus. We studied the percentage of pregnant women in our hospital with antibodies to HCV, and tried to compare the C100-3 antibodies with PHA results in pregnant women. The results are as follows. 1) In the sera of 235 pregnant women both the PHA antibody and the C100-3 antibody were examined. Two women (0.85%) had the C100-3 antibody and 4 (1.7%) had the PHA antibody. 2) Two women positive for both PHA and C100-3 antibodies were positive for PCR during pregnancy. But 2 women positive for PHA only were negative for PCR during pregnancy and positive after delivery. So 4 women positive for PHA had HCV RNA. 3) Next, the sera of 1,198 pregnant women were examined by the PHA method, and nine women were positive. Only four of the 9 were positive for C100-3. 4) It is speculated that the positive rate for anti-HCV antibodies in the sera of pregnant women in Nagoya city is 0.75%. 5) There were 3 cases that were negative for PCR during pregnancy and positive after delivery. So it is speculated that HCV can be activated after delivery.