Polymerase chain reaction (PCR) assays for the detection of variousFusarium species and Microdochium nivale subspecies were compared with conventional visual disease assessment using a field plot of wheat in which the central subplot was inoculated with F. culmorum. Visual disease assessment was performed on a range of samples taken from each of 15 subplots at growth stage 80. At harvest, each sample was divided into its component parts, i.e. grain, glume and rachis, and species-specific PCR analysis was used to detect the presence of F. culmorum, F. poae, F. avenaceum, F. graminearum, M. nivale var.majus and M. nivale var. nivale. Within the inoculated subplot there was good correlation between visual disease assessment and PCR analysis, both techniques indicating a high incidence of F. culmorum in this region. According to the visual disease assessment results, there was also a relatively high incidence of F. culmorum in most other regions of the field plot. However, according to PCR analysis the incidence of F. culmorum in many of the other subplots was relatively low and F. Poae, M. nivale var. majus and var. nivale, and F. avenaceum were detected within the grain, glume and rachis tissues of many of the ear samples from these subplots. F. poae predominated in the glume component of ears andM. nivale var. majus and var. nivale in the rachis component. M. nivale PCR results revealed that 64% of infected samples involved var. majus, and 36% var.nivale. PCR analysis has highlighted some difficulties that may arise when using visual assessment for studying disease complexes.