Orungo and Lebombo orbivirus isolates were examined for their intra- and intergroup genetic relatedness by blot hybridization and gene reassortment; blot hybridization was also used to examine the relatedness of selected Orungo and Lebombo isolates to known orbiviruses. Among the Orungo isolates, greater than 74% sequence similarity was shown in the majority of their genes. Gene 2 was the most divergent gene, with four unique types identified, and genes 5, 6 and 10 were variant among the isolates. Plaque reduction neutralization tests revealed at least four serotypes, a result which correlated with the hybridization data. Gene reassortment was shown between two representative Orungo isolates. Among the Lebombo isolates, two hybridization types were identified between which gene reassortment was demonstrated. Unique genes were not shown, whereas genes 2, 5 and 10 exhibited minor sequence variability. Geographic distribution correlated with relatedness among the Lebombo isolates, which was not the case among the Orungo isolates. Orungo and Lebombo viruses did not cross-hybridize or reassort their genes in vitro, in intergroup studies. In blot hybridization tests of Orungo and Lebombo isolates with known orbivirus serogroups and ungrouped orbiviruses, no strong cross-hybridization was seen. These results demonstrate that Orungo and Lebombo are distinct from each other and from other orbiviruses, and should therefore be recognized as two new Orbivirus serogroups.