Surveys of wheat fields in West Central Morocco showed average root rot severity indices of 7.2 and 10.8%, and yield losses of 4 and 6% in 1985/86 and 1986/87 seasons respectively. The most prevalent fungi associated with root rot symptoms were Helminthosporium sativum, Fusarium equiseti, F. culmorum, F. oxysporum, and F. solani. Of these F. culmorum and H. sativum are recognized as pathogens of wheat. Fusarium equiseti was the most prevalent in soils followed by F. solani and F. oxysporum. The pathogenic species F. culmorum, F. graminearum, and F. avenaceum were found in a few fields. Fusarium equiseti was the most prevalent on wheat seed and F. culmorum, F. graminearum, and H. sativum occurred at low frequencies. These data suggested that soil was the major source of inoculum for the root rot pathogens of wheat;The relative importance of seed and soil as sources of inoculum was investigated. Soil-borne inoculum of both F. culmorum did not affect seedling emergence but did cause root rot and reduced grain yield. Low levels of F. culmorum natural seed-borne inoculum did not induce root rot but high levels of artificially applied seed-borne inoculum of this fungus caused severe root rot and drastic reduction in seedling emergence and crop yield;Factors that affect wheat root rot were investigated. High planting density tended to increase root rot and deadhead incidence. Seed vigor had no effect on root rot development and crop yield. Thiabendazole seed treatment eradicated F. culmorum inoculum from seed; controlled root rot; improved emergence, straw and grain yield; and reduced infection from soil-borne inoculum of this fungus. Of the varieties tested, Cocorit was highly susceptible to F. culmorum and Kyperounda was moderately susceptible H. sativum. Marzak, Karim, and Kyperounda were moderately susceptible to F. culmorum while Cocorit, Marzak, and Karim were fairly resistant to H. sativum. Higher root rot incidence and severity, and greater crop loss were detected in 1986/87 dry season than in the wetter 1985/86.