Partial soil sterilization with Picfume, Vapam, Vorlex, Terraclor, Telone and combinations of Telone and Picfume have been included in studies for one or more years between 1960 and 1963. All the chemicals tested except Terraclor resulted in yield increases statistically and economically larger than the yields of potatoes produced on the untreated check plots. Partially sterilizing the soil in the fall resulted in large increases in yield of potatoes the following year. The effect of the partial sterilization of the soil lasted for at least two years. The causes for the increases in yield are not known. “Early dying” disease caused byVerticillium alboatrum was known to be present, but increases in yield also resulted from the use of Telone which is predominantly a nematocide. Pathogenic nema were few in number. A combination of Picfume and Telone, economically feasible in Washington, produced large yield increases over a two-year period and did not produce an off flavor in the potatoes when applied in the fall.