Forty fetuses who had mild or marked tachycardia during the final 10 minutes of the second stage of labor were evaluated for neonatal infection. Prolonged sepsis/pneumonia occurred in 10 of the 40 infants (25%), three of eight (38%) with marked tachycardia, seven of 32 (22%) with mild tachycardia, and in only one of 167 control infants who had a normal second-stage fetal heart rate (0.6%). None of the 40 women with fetal tachycardia or the 167 control subjects had any intrapartum fever or other evidence of acute chorioamnionitis. Persistent fetal tachycardia during the second stage of labor defines a population at increased risk for subsequent neonatal sepsis/pneumonia. This population will require prolonged, expert neonatal care. © 1984.