Burley tobacco plants were severely reduced in growth when transplanted into soils infested with nonviablePhytophthora cryptogea. Soils that were infested with the fungus and then sterilized by autoclaving or methyl bromide fumigation stunted tobacco transplanted into them. Mycelium produced on a defined medium and lyophilized, powdered, and mixed with soil was toxic to plants at between 0.5 and 1.0 g per 400 grams of soil. These results provide direct evidence that severe reduction in growth of Burley tobacco caused byP. cryptogeais not due to parasitism.