Development of the disease Alternaria leaf blight (Alternaria carthaml) on safflower (cv. Gila) and its subsequent effect on yield, yield components and seed quality were assessed in the field at Biloela in central Queensland in 1976. Two seed types, one affected with A. carthami and the other healthy, were used. Seedlings from both were sprayed either with the fungicide mancozeb to control the disease or with an equivalent amount of water. Sprays were applied weekly from thinning, 3 weeks after planting, until maturity 21 weeks later. In the water treatments, the disease developed slowly from emergence in June to budding in early August, then rapidly during the period from late August to October as temperature and humidity increased. Repeated use of the mancozeb spray was more effective than the use of healthy seed in controlling the disease, as yields in the treatments sprayed with fungicide were similar. Yields in the diseased and healthy seed treatments sprayed with water were 44% and 57%, respectively, of the mean yield of the treatments sprayed with fungicide. Seed per tertiary head, and weight of secondary and tertiary seed, were most affected by the disease. In addition, oil and protein concentration were markedly depressed as were grain and volumetric weights. Differences in oil composition were not considered important.