Kinetoplast DNA occurs in flagellated protozoa belonging to the order Kinetoplastida. Kinetoplast DNA contains tens of maxicircles and thousands of minicircles which are catenated into a single network in each cell. Maxicircles contain genetic information analogous to that in other mitochondrial DNAs. Maxicircles encode mitochondrial ribosomal RNAs and hybridize with mitochondrial gene sequences from other organisms. Minicircles evolve rapidly, may not be transcribed, and vary greatly in total complexity among genera. The functions of minicircles and the network structure are unknown.