The growth, development, chemical composition and nutritive value of sunflower (cv. Fransol), was examined from the flower-bud (12 July) to milky-ripe seed (late September) stages. Dry-matter yield increased from 2-1 to 14-1 t/ha over the period. Dry-matter content was low (100-110 g/kg) up to flowering, early in August, and then increased to 193 g/kg. Crude protein content declined after flowering and ether extract values were low throughout the period. Organic-matter digestibility in vitro and derived metabolizable energy values declined rapidly with the onset of flowering. Gross energy values, calculated from the proximate constituents, increased to 17-6 MJ/kg d.m. at the end of the period. Calcium to phosphorus ratios varied from 5-6 to 7-4:1.Sunflower was cut and fed to eight Friesian heifers over 3 weeks from the onset of flowering. Average daily d.m. intake was 63-5 g/kg W0.76 and the organic-matter digestibility was 0-684. Average live-weight gain was 0-79 kg/day. Fresh sunflower was successfully ensiled without an additive 2 weeks after flowering and the silage (pH 4-0) was fed to three cross-bred wethers in a feeding trial. The organic -matter digestibility was 0-649, the metabolizable energy 80 MJ/kg d.m. and the average d.m. intake 67-3 g/kg W0'76. In a metabolism trial, with four fistulated sheep, the organic-matter digestibility was 0-718, the metabolizable energy 9-4 MJ/kg d.m. and the d.m. intake 43-1 g/kg W076. Rumen pH decreased and total volatile fatty acid concentration increased markedly within 2 h of feeding the silage. Molar proportions of acetic and propionic acid (0-539 and 0-381), 1 h after feeding, were typical of cereal-based diets. Ammonia-nitrogen concentration increased to a maximum of 216 mg/1 within 2 h of feeding. The good yield and animal performance from fresh sunflower make it a possible annual crop for zero-grazing in late summer in northern Britain. Satisfactory results from feeding sunflower silage suggest that the crop has potential for ensilage if the problem of effluent can be overcome.