A grazing experiment with a switch-back design was used to evaluate the response to sulphur supplement by 18 lactating cows grazing a 5 to 7 week growth of sorghum x Sudan grass hybrid (cv. 'Sudax X11a'). The forage dry matter contained 0·12 to 0·15 per cent sulphur and nitrogen to sulphur ratios of 15·0 to 17·5 : 1. Hydrogen cyanide potential of the forage ranged from 0·009 to 0·022 per cent of dry matter and probably reduced the availability of sulphur. Sodium content of the forage was low averaging 0·03 per cent of dry matter. Milk yield and protein content of milk were increased by sulphur supplementation probably due to an increased intake of organic matter.