['Telbivudine reduces hepatitis B virus (HBV) DNA and normalizes levels of alanine aminotransferase (ALT) in patients with chronic hepatitis B (CHB). We investigated its use in preventing vertical transmission.', 'We performed an open-label, prospective study of 88 hepatitis B (HB) e antigen (HBeAg)-positive pregnant women with CHB, levels of HBV DNA >6 log(10) copies/mL, and increased levels of ALT. Women were given telbivudine (n = 53) starting in the 2nd or 3rd trimester, or no treatment (controls, n = 35) and followed until postpartum week (PPW) 28. All infants received standard immunoprophylaxis after birth.', "At 28 weeks, none of the infants whose mothers received telbivudine had immunoprophylaxis failure, whereas 8.6% of the infants of control mothers did (P = .029). There were no differences between groups in mothers' adverse events or infants' congenital deformities, gestational age, height, and weight, or Apgar scores. At postpartum week 28, significantly more telbivudine-treated mothers had levels of HBV DNA <500 copies/mL, normalized levels of ALT, and hepatitis B e antigen seroconversion compared with controls (58% vs none, P < .001; 92% vs 71%; P = .008; and 15% vs none; P < .001, respectively) but none had loss of hepatitis B surface antigen. Telbivudine-treated mothers had no virologic breakthrough (HBV DNA >1 log(10) increase from <500 copies/mL) or discontinuations from adverse events. After delivery, 13/52 patients discontinued telbivudine due to preference. There were no episodes of severe hepatitis (levels of ALT >10 times the upper limit of normal) in either group during 28 weeks of postpartum observation."] Does telbivudine prevent vertical transmission from HBeAg-positive women with chronic hepatitis B?