The maternal-fetal transfer of Salbutamol was studied in vitro, in dual perfusion of isolated human placental lobules. The fraction of drug transferred to the fetal side was compared to reference substances: (14C)-antipyrine and (3H)-inulin. Salbutamol transfer( 12 %) represents about 39 % of antipyrine and five times of inulin transfer. Studies with varying Salbutamol concentrations in the maternal arterial perfusate revealed that the drug transfer to the fetal side was effected by a flow-dependant diffusion process. We conclude that the reported effects on the fetus following a maternal drug infusion are mediated by the drug transferred accross the placenta.