Tobacco was fumigated for 96 hours with phosphine, at the rate of 165 pellets aluminum phosphide per 1000 cubic feet, in cases lined with four different materials. Fumatorium air space phosphine concentrations reached 1200 ppm after 72 hours fumigation. Peak measurements in lined cases were 185 ppm in 4 mil. polyethyline lined cases, 293 ppm in 6 mil. polyethylene lined cases, both after 96 hours of fumigation. 288 ppm in poly duplex lined cases, and 440 ppm in asphalt duplex lined cases, both after 72 hours of fumigation. In unlined control cases, average peak measurements were 958 ppm after 72 hours of fumigation. Unlined cases aerated rapidly. Aeration of lined cases was slow with concentrations greater than 9.1 ppm recorded after 288 hours aeration. Fumigation for 96 hours is recommended for lined cases to achieve effective within case concentrations. Aeration for 48 hours will ensure worker safety following warehouse fumigation of lined and unlined cases.