In this investigation, thyroid hormone levels and blood pH were compared in 10 newborn lam bs and in their dams immediately at parturnion then 24 and 72 h therealter. The blood pH was lower and serum thyroid hormone levels were higher in the newborn lambs than those in the sheep. In the lambs, blood pH and serum total Iri· iodothyronine (TT₃) levels increased at 1h, 24h and 72h postpartum, whereas serum total thyrexine (TT₄) levels in the lambs decreased over time. The corresponding paramaters did not change over time in the case of sheep exeapt that there was a decline serum TT₃ levels at 72h postpartum. Especially, significant (P<0.05) negative correlation was found between thyroid hormone levels and blood pH in the lambs 24 and 72h postpartum.