Serum levels of retinol, 25-hydroxyvitamin D2, 25-hydroxyvitamin D3 and α-tocopherol were determined by high performance liquid chromatography from 142 Standardbred and Finnish Coldblooded Trotters aged three to 15 years. Blood samples were collected during January and July. Serum levels of retinol and α-tocopherol were about a third of those in man, with summer values indicating an increase in most horses. The relatively low serum concentrations of 25-hydroxyvitamin D and α-tocopherol suggest that during the winter season a deficiency of these vitamins may occur in horses in northern countries such as Finland. Significant differences were observed between values of horses from different stables, especially for serum α-tocopherol. The differences probably reflect differences in the quality of feeds and/or different feeding practices.