Two runner-type peanut cultivars, “Sunbelt Runner” and “Florunner,” were compared under differing field conditions for contamination of the seed by Aspergillus flavus Link and aflatoxin. Laboratory tests had shown marked differences in resistance between the two cultivars. Peanuts were grown on three nonirrigated farms during 1980 using two planting dates and three harvest dates for each cultivar. Peanuts grown on two farms experienced moderate to severe drought stress and both cultivars contained high levels of aflatoxin. Peanuts on the third farm received adequate rainfall and contained very low levels of aflatoxin. Microflora, grade and aflatoxin data showed that Sunbelt Runner (reported to be resistant to A. flavus infection) had no advantage over Florunner (reported to have moderate resistance to A. flavus) in reducing levels of A. flavus and subsequent aflatoxin contamination under field conditions. Levels of infection and contamination were related primarily to environmental conditions, (especially drought stress), during pod maturation. These and prior results show that the current laboratory assay method for selecting resistant lines should be carefully reassessed.