During the 1995-96 growing season, the effects of fertiliser application and growth of different crops on the population of Fusarium oxysporum f. sp. vasinfectum (Fov) in field soils were examined. In soil samples collected 35 days after fertiliser application, densities of Fov were significantly lower in soils receiving 180 units of anhydrous ammonia than in those receiving 40 or 180 units of urea. When compared with samples collected at sowing, densities of Fov were significantly reduced in soil samples from plots planted to either the less susceptible cotton cultivar DP90 or soybean. The proportions of Fov in the total F. oxysporum population increased significantly in soils planted to the most susceptible cotton cultivar Siokra 1-4, but decreased significantly in soils planted to the less susceptible cultivar DP90.