Relations between leaf rust progress, foliage senescence and yield reduction were studied for seven winter wheat genotypes, differing in their partial resistance to leaf rust. Leaf rust accelerated leaf and ear senescence. Photosynthesis measurements showed, however, that the photosynthetic capacity of the remaining green surface was not affected. Differences between genotypes in yield reduction were largely explained by differences in leaf senescence and, therefore, in cumulative light interception (r = 0.83) and crop photosynthesis. Reduction in cumulative light interception was closely related to the area under the disease-progress-curve (r = 0.85), which was also closely associated with yield reduction (r = 0.88). However, the time taken to reach a 501t!o reduction of green leaf area and the pustule density on I July (i.e. halfway through the epidemic) were just as good predictors of yield reduction as cumulative light interception and area under diseaseprogress-curve, suggesting that the former are useful criteria in the selection for partial resistance to leaf rust.