We have constructed a fragment map of the maxi-circle component from kinetoplast DNA networks of Trypanosoma brucei brucei (East African Trypanosomiasis Research Organization strain No. 427), using restriction endonucleases PstI, HapII, EcoRI, BglI, HindIII, HhaI, SstI, XbaI, HaeIII and Sau-96I. Although the 20 kilo-base pair map contains 30 fragments, there is a 6.5 kilo-base pair 'silent' segment which lacks recognition sites for any of these enzymes. In CsCl intact kinetoplast DNA has a buoyant density of 1.690 g/cm3, whereas a kinetoplast DNA fraction enriched in maxi-circle sequences contains an additional component at 1.682 g/cm3. The possibility that the 'silent' segment is very rich in A + T is discussed.