Aspergillus flavus produces the potent carcinogenic compound, aflatoxin, in cottonseed in the field. To determine conditions conducive to Aspergillus flavus infection of cottonseed in undamaged bolls, cotton plants were grown in 1.5 m PVC pipes and subjected to various levels of water and nutrient stress. Flowers were inoculated on the involucral nectaries, the resulting individual bolls harvested, lint and seed weighed, and the seed assayed for A. flavus on agar plates. Under these greenhouse conditions, we were able to mimic field conditions closely enough to obtain A. flavus infection in undamaged bolls. Water stress was the most important controlled variable for A. flavus infection. Under high water stress conditions, yield and seed weight were significantly higher in plants and bolls with A. flavus infected seed.