We monitored plasma epinephrine and norepinephrine responses to hemorrhage of 20% of estimated blood volume in 11 chronically instrumented, unanesthetized fetal lambs. In addition, we performed control experiments--blood sampling but no hemorrhage--in five fetuses. Arterial blood gases, pH, mean arterial pressures, heart rates, and plasma norepinephrine and epinephrine levels were similar in both groups in the resting state. Arterial blood gases and pH did not change significantly during the experimental period in either group. Mean arterial pressure, heart rate, and plasma norepinephrine and epinephrine levels did not change in the control group during the experimental period. Hemorrhage was associated with a significant decrease in fetal mean arterial pressure, 39.8 +/- 1.2 to 29.6 +/- 2.1 mm Hg, and heart rate, 186 +/- 8 to 146 +/- 6 bpm (p less than 0.01 in both cases). There was a significant increase in plasma norepinephrine, 664.9 +/- 91.6 to 1384.8 +/- 216.7 pg/ml (p less than 0.02) and epinephrine, 224.6 +/- 43.6 to 681.7 +/- 199.0 pg/ml (p less than 0.01) with hemorrhage. These results demonstrate significant catecholamine responses to hypovolemia in the fetal lamb.