The effects of Fusarium oxysporum f.sp. vasinfectum (FOY) and Meloidogyne incognita (MI) on seed cotton yield, plant mortality and nematode reproduction in the cotton cultivar TAMCOT SP37 were assessed in field microplots during the 1985 and 1986 growing seasons. In 1985, the soil was infested with two levels of FOY (14,000 and 21,000 cfu/g soil and four levels of MI (0.1. 1.0, 10, and 50 nematodes/100 cmi soil). Plant mortality was assessed at 2-wk intervals. Seed cotton yield was based on the combined weights of two harvests. During the 1985 season there was a main effect of FOY early in the season (approximately 8-10 wks post-planting) and it remained constant for the remainder of the season. There was no difference in effects of the two FOY levels. There was also a significant and increasing effect on plant mortality later in the season (16-22 wk post-planting) at the highest MI level, but not at the lower nematode levels. There was no significant FOY x MI interaction at any single assessment time.