Excerpts from the report Summary: To evaluate the effectiveness of the three basic methods of fumigation—gravity-penetration, single-pass, and closed-recirculation—three identical flat-storage Behlen buildings and three identical flat-storage Butler buildings, each containing about 100,000 bushels of wheat, were treated with methyl bromide at the rate of 2 pounds per 1,000 cubic feet. Distribution of the methyl bromide and the resulting mortality of test insects were determined in more than 100 sample locations in each building. Superiority of the closed-recirculation method is clearly demonstrated by the data on fumigant distribution and insect mortality. The difference in results justifies the expense of adding return ducts to existing aeration systems to permit recirculation of the fumigant. The effectiveness of the gravity-penetration and single-pass fumigations was limited by the lack of uniformity in distribution of the fumigant concentrations.