It has been suggested that there exists carrier mediated diffusion for carbon monoxide and oxygen in the lung and placenta. Using a breathholding technique in newborn lambs, we will measure pulmonary diffusing capacity for carbon monoxide (Dlco) at three different CO concentrations. In a perfused in vivo placental preparation, we will measure CO diffusion at three different CO concentrations. A fall in diffusion at the higher CO concentrations would provide good evidence for carrier mediated transfer. Dlco will be measured in three groups of lambs: 0.7, 0.8, and 0.9-1.0 duration of pregnancy. In this way the diffusing capacity of the developing lung will be evaluated. In addition, the effects of certain obstetrical analgesic agents on newborn Dlco will be measured.