Technical Abstract: Contamination of maize (Zea mays L.) grain with aflatoxin, produced by the fungus Aspergillus flavus Link:Fries, or fumonisin, produced by the fungus Fusarium verticillioides (Saccardo) Nirenberg (Syn=F. moniliforme Sheldon), greatly reduces its value and marketability. Host resistance to fungal infection and mycotoxin accumulation is considered a highly desirable way to reduce losses of both aflatoxin and fumonisin. Maize germplasm lines with resistance to aflatoxin accumulation have been developed in Mississippi. Three of the aflatoxin-resistant lines and five additional lines were used as parents to produce a diallel cross. The diallel cross was evaluated for fumonisin accumulation in field tests conducted in Mississippi in 2007 and 2008. General combining ability (GCA) was a highly significant source of variation in both 2007 and 2008, but specific combining ability (SCA) was not significant. GCA effects for reduced fumonisin levels were highly significant for Mp715, Mp717, and GA209. Mp715 and Mp717 were developed and released as sources of resistance to aflatoxin contamination and exhibit resistance as inbred lines and in hybrid combinations. These lines should be useful in developing maize lines and hybrids with resistance to both fumonisin and aflatoxin accumulation in grain. Breeding methods that maximize the use of GCA should be useful in enhancing resistance to both fumonisin and aflatoxin accumulation. GA209 also exhibited favorable GCA for resistance to fumonisin accumulation, but this line is highly susceptible to aflatoxin accumulation. If used in breeding programs to develop maize with resistance to fumonisin accumulation, care to avoid increasing susceptibility to aflatoxin accumulation would be needed.