The effects of fetal hypoxemia on blood coagulation (platelet count, prothrombin time, partial thromboplastin time, fibrinogen, factors II, V, VI, VIII, IX, X, XI, XII, XIII and von Willebrands activities, fibrin degradation products, and fibrin monomer) were evaluated in nine chronically catheterized fetal lambs early in the third trimester of pregnancy (107-110 days gestation). Seven chronically catheterized fetal lambs of similar gestational ages served as controls. The hypoxemic episode (pO2 14 mm Hg) was maintained for 1 hr in the experimental group during which time there were only minimal changes in PCO2, arterial pressure, heart rate, and pH. Epinephrine and norepinephrine levels increased significantly in stressed animals--22 pg/ml pre- to 1025 pg/ml postepinephrine, and 475 pg/ml pre- to 2292 pg/ml postnorepinephrine. There were no significant changes in blood coagulation factor activities related to the hypoxic stress although, one fetus who experienced acidemia did develop a transient increase in fibrin monomer. Slight through significant increases in VIII coagulant activity activity (4.0%), von Willebrand activity (5.9%), and factor XII activity (4.3%) occurred in both the hypoxemic and control fetal lambs. These changes were associated with minimal increases in the white blood cell count (15%) and slight decreases in the mean arterial pressure (3.9 mm Hg) hemoglobin (1.2 g), and hematocrit (2.9%) and may have been related to the blood loss of 25% that occurred as a result of sampling in both groups. There were no differences between the hypoxic and control animals' levels of coagulation factor activities when measured during an 18-day follow-up period except for a slight increase in factor X activity (10%) in the control animals not apparent in the nine hypoxic animals. Thus an episode of severe fetal hypoxemia in the absence of hypotension, acidosis, and hypercarbia does not lead to acute or chronic alterations in blood coagulation factor activities in the fetal lamb.