In the order Kinetoplastida, genetic exchange has been demonstrated only in the genus Trypanosoma. Analysis of kinetoplast DNA (kDNA) in genetic crosses of T. brucei has shown that whereas maxicircles are inherited uniparentally, minicircles are inherited from both parents. This result was confirmed for a new cross of T. b. brucei and T. b. rhodesiense by restriction enzyme digestion and Southern analysis of purified kDNA. By hybridisation with small minicircle-derived probes, we could demonstrate the presence of particular parental minicircles in the kDNA of hybrid progeny clones. All hybrid clones had inherited two minicircles from one parent despite two of the four clones having maxicircles from the other parent. The results suggest that rather than small-scale exchange of minicircles between parental networks, gross breakdown and reassembly of the minicircle network occurs during genetic exchange.