Cotton cultivars Acala SJ-2 and Acala SJC-1, and cotton lines N6072 and N8577, were used in field studies located in the U.S. Cotton Research Station, Shafter, CA. Replicated split plots with varying levels of pathogens Fusarium ozysporum f. sp. vasinfectum (Fov) and Meloidogyne incognita (Mi) were used for the comparison of susceptibility and disease development in cotton selections which differed in reaction to Fov and Mi. The interaction of Fov and Mi with host plants was determined by their density in soil and by isolation of Fov from serial sections of stem and leaf tissues, as well as by nematode root galling and by folair symptoms of Fusarium wilt. Colonization of host tissue by Fov and the incidence of foliar symptoms of wilt were evident in the presence of a low Mi population in all four cotton selections. However, the frequency of isolation of Fov in cotton plants was increased in the presence of a high Mi population. The influence of soil-borne densities of fungal propagules and nematode populations of differences in host susceptibility and disease development will be discussed.