Platelet activation has been implicated in the pathogenesis of several obstetrical conditions such as preeclampsia and intrauterine growth retardation. Plasma beta-thromboglobulin (BTG) concentration is an index of in vivo platelet activation. The purpose of this study was to establish normal values of plasma BTG during pregnancy, labor and puerperium. Plasma BTG concentrations were determined from 121 uncomplicated pregnant women, 20 women in labor, 20 puerperal women, and a control group of 28 healthy non-pregnant volunteers. There was no significant difference in plasma BTG concentrations between non-pregnant and pregnant women. Gestational age, labor, and puerperium did not affect plasma BTG concentrations.