Charcoal rot of sorghum, caused by the fungus Macrophomina phaseolina, is a severe disease in regions where sorghum encounters post-anthesis drought stress. Previous reports disagree with respect to the narure of the genetic factors that condition resistance to charcoal rot. A diallel cross was made using nine genetically diverse sorghum lines. Parental lines and Fl progenies were evaluated in the field in 1997 and 1998 at two locations. Lines were significantly more resistant than Fls, indicating that heterosis was not affecting resistance. General combining ability (GCA) and specific combining ability (SCA) effects were significant for both locations over both years. However, the magnitudes of SCA effects were much smaller than GCA effects. These observations indicate that resistance to charcoal rot is conditioned by both additive and nonadditive effects.