The clotting parameter of a primigravida with factor XII deficiency was studied during her third trimester of pregnancy, labor and post-partum; and compared with those of her newborn male infant. Sharp increases in factors VII, VIII, IX, X and moderate increases in factors II and XI were documented during pregnancy and at labor. All factors had returned to normal or near normal levels 24 hours after delivery. Factor XII remained at 0.0 level throughout. In the infant the clotting factor levels reflected depression of vitamins K-dependent factors II, IX, and X and a factor XII level of 40.0%. No undue bleeding was noted in the mother at delivery or placental separation, and no bleeding manifestation was apparent in the infant. These findings suggest that factor XII does not play a major role in triggering or modulating the course of normal labor, nor is its absence necessarily associated with bleeding complications during parturition or placental separation.