Liver function tests (GOT, GPT) were performed on 269 female HB virus carriers during pregnancy and puerperium with the following results: Pregnancy in HB virus carriers did not result in any deterioration in liver function, but was rather associated with its gradual normalization particularly in symptomatic carriers. At 1 month of puerperium, in contrast, the occurrence or rebound flare-up of hepatitis was frequently observed among the virus carriers, notably with overt liver dysfunction being seen in 43% of those positive for e antigen. Of 28 e antigen-positive carriers in whom a follow-up study was extended to the next pregnancy, 12 whose liver function was normal during puerperium had normal liver function during the next pregnancy and was positive for e antigen. In the other 16 carriers showing deteriorated liver function during puerperium, liver function during the next pregnancy was abnormal in 6 and normal in 10, with seroconversion and negativity for e antigen being observed in 2 and 4, respectively, of these 16. It is inferred that fluctuations in liver function and e antigen during pregnancy and puerperium might be consequent on increased secretion of corticoids during pregnancy.