The mitochondrial DNA (mtDNA) of a primitive kinetoplastid flagellate Cryptobia helicis is composed of 4.2 kb minicircles and 43 kb maxicircles. 85% and 6% of the minicircles are in the form of supercoiled (SC) and relaxed (OC) monomers, respectively. The remaining minicircles (9%) constitute catenated oligomers composed of both the SC and OC molecules. Minicircles contain bent helix and sequences homologous to the minicircle conserved sequence blocks. Maxicircles encode typical mitochondrial genes and are not catenated. The mtDNA, which we describe with the term 'pankinetoplast DNA', is spread throughout the mitochondrial lumen, where it is associated with multiple electron-lucent loci. There are approximately 8400 minicircles per pankinetoplast-mitochondrion, with the pan-kDNA representing approximately 36% of the total cellular DNA. Based on the similarity of the C.helicis minicircles to plasmids, we present a theory on the formation of the kDNA network.