Reductions in fetal plasma concentrations of certain amino acids and reduced amino acid transport in vesicle studies suggest impaired placental amino acid transport in human fetal growth restriction (FGR). In the present study we tested the hypothesis of an impairment in amino acid transport in the ovine model of hyperthermia-induced FGR by determining transplacental, placental retention and total placental clearance of a branched-chain amino acid (BCAA) analogue, the nonmetabolizable neutral amino acid, aminocyclo-pentane-1-carboxylic acid (ACP), in singleton control (C) and FGR pregnancies at 135 days gestation age (dGA, term 147 dGA). At study, based on the severity of the placental dysfunction FGR fetuses were allocated to severe (sFGR, n=6) and moderate FGR (mFGR, n=4) groups. Fetal (C; 3801.91 ± 156.83, mFGR; 2911.33 ± 181.35, sFGR; 1795.99 ± 238.85 g, p<0.05) and placental weights (C; 414.38 ± 38.35, mFGR; 306.23 ± 32.41, sFGR; 165.64 ± 28.25 g, p<0.05) were reduced. Transplacental and total placental clearances of ACP per 100 g placenta were significantly reduced in the sFGR, but not in the mFGR group, while placental retention clearances were unaltered. These data indicate that both entry of ACP into the placenta and movement from the placenta into fetal circulation are impaired in severe ovine FGR and support the hypothesis of impaired placental branched-chain amino acid transport in severe human FGR.