Effects of pantethine (PaSS) on serum levels of lipids of rats and chicks have been examined : PaSS, when administered orally in a daily dose of 1g/kg for 10 days, decreased serum cholesterol levels of the rats fed on normal diet. One-week administrations of PaSS inhibited the increase of serum cholesterol levels produced by feeding rats on high-cholesterol diet, while the effect was not clear in case of two- and three-week administrations of the compound. In chicks fed on high-cholesterol diet, PaSS was found to suppress the increase of serum levels of phospholipid and triglyceride as well as that of cholesterol. In addition, suppression of pathological changes in the aorta and liver of the animals has also been observed by administration of PaSS.