Calf satellite DNA I (p = 1.715) has been hydrolysed by a number or restriction endonucleases. It consists of a repeating unit of 1460 nucleotide pairs within which the sites of Eco R II Mbo I, Sac I, Alu I, Ava II and Hha I were localised in comparison with those of Eco R I and Hind II. The distribution of the Hpa II, Sac I, Hha I, Hinf I and Mbo II sites within calf satellite DNA I, as well as that of several restriction endonuclease sites within calf satellite DNA III (p = 1.705) allowed me to define subsatellite fractions. Furthermore, some of the sites of the CpG containing restriction enzymes Hpa II and Hha I are lacking. The possible implications of these results are discussed.