Uptake of alpha amino isobutyric acid was measured in human placental villus tissue exposed in vitro to ethyl alcohol (ethanol) (0.3 g/dl-2 g/d1) or acetaldehyde (50 μM-20 mM). Ethanol and acetaldehyde significantly inhibited uptake of amino acid at higher, pharmacologic concentrations (2 g/dl and 2-20 mM respectively). Inhibition by 10 mM acetaldehyde was partially reversible. The results suggest that the human placenta is resistant to acute ethanol-associated effects upon amino acid transport in vitro. However, both ethanol and its major circulating metabolite, acetaldehyde, may still alter placental function during in vivo chronic exposure.