In eight patients with biopsy-confirmed chronic active hepatitis (CAH), hepatitis B e antigen (HBeAg) levels and DNA polymerase (DNA-P) activity were assayed three times a week for six weeks and once a week for another six weeks. HBeAg levels were rather constant, whereas DNA-P activity fluctuated. No correlation was observed between the quantities of HBeAg and DNA-P activity. An unexpected fluctuation in DNA-P activity was noted in all patients after an influenza vaccination.