An experiment designed to study the response in milk production to dried grass given as an addition to a basal roughage diet and to assess its value as a replacement for conventional dairy concentrates is described. A randomized block design with 34 lactating cows was used. The cows received supplements of either dried grass (dry-matter digestibility, 70%, 0·28, 0·39, 0·50 or 0·61 kg/kg milk) or a cereal-based dairy concentrate (0·39 kg/kg milk) in addition to silage offered in amounts to meet the maintenance energy requirements. Milk yield, milk energy output, live-weight gain and the fat, solids-not-fat and protein contents of the milk increased with level of addition of dried grass. Interrelationships between the level of feeding of dried grass and milk output and body-weight change are given. The derived relationships between dried grass input and animal output were used to predict the replacement value of dried grass for conventional dairy concentrates. These indicated that dried grass offered at 042 kg/kg milk would produce equivalent milk yield and body-weight changes to concentrate given at 0·39 kg/kg milk. Ration digestibility and nitrogen balance results are also given.