The cleavage of kinetoplastic DNA (kDNA) with the restriction endonucleases (Eco RI, Hind II + III, Hpa II) was studied. The quantitative data of electrophoretically separated fragments show that the kDNA (free circular genome units and complex network) is composed of distinct populations of circles. Kinetic studies of renaturation of kDNA previously cleaved by Hpa II into fragments having the length of one genome unit also indicate the presence of at least two and probably three populations of molecules.