A one-year clinical trial with pantethine was conducted in 24 patients with established dyslipidemia of Fredrickson's types II A, II B, and IV, alone or associated with diabetes mellitus. The treatment was well tolerated by all patients with no subjective complaints or detectable side effects. Blood lipid assays repeated after 1, 3, 6, 9, and 12 months of treatment revealed consistent and statistically significant reductions of all atherogenic lipid fractions (total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B) with parallel increases of high-density lipoprotein cholesterol and apolipoprotein A. The results were equally good in patients with uncomplicated dyslipidemia and in those with associated diabetes mellitus. The authors conclude that pantethine (a drug entity related to the natural compound, pantetheine) represents a valid therapeutic support for patients with dyslipidemia not amenable to satisfactory correction of blood lipids by diet alone.