To evaluate contributions of catecholamines to inhibition of growth during chronic hypoxemia or severe undernutrition, epinephrine (Epi; 0.25-0.35 µg · kg¹ · min¹) or norepinephrine (NE; 0.5-0.7 µg · kg¹ · min¹) was administered to normoxemic fetuses in twin-pregnant ewes for 8-12 days, from 125 to 127 days of gestation. Both had similar effects and decreased fetal weight by ~20% relative to control twins (P < 0.01). Weight gain ceased during infusion of Epi or NE (21 ± 14.8 or 14 ± 20.9 g/day), whereas controls gained 93 ± 13.2 g/day (P < 0.01). Effects on tissues and organs varied, spleen and thymus being most retarded, whereas brain weight and skeletal measures were affected little. Selected muscles from infused fetuses weighed 72% of those in controls. Growth ceased during infusion (P < 0.001). Weight gain of hindlimb bones was negligible, but length increased at 56% of control rates. Arterial blood CO₂ and plasma insulin were decreased (P < 0.001), but plasma glucose, growth hormone, and blood oxygenation increased (P < 0.001). Actions of Epi and NE could underlie asymmetrical growth retardation occurring in many adverse physiological situations during fetal development.