The increasing interest in the potential of forage mixtures for milk production in the UK resulted in a three year study being commissioned at the Centre for Dairy Research by the Milk Marketing Board. Year 1 compared the effect on forage intake and yield of milk and milk constituents of replacing grass silage (GS) with either fodder beet (FB), urea-treated (4%) (UW) or fermented whole-crop wheat (FW) or brewers grains (BG) at 330 g/kg of forage DM or maize silage at either 330 (MS) or 750 (MSH) g/kg forage DM. All cows received 6 kg DM/day of an appropriate concentrate so that dietary crude protein (CP) was equalised. Tire use of forage mixtures significantly increased DM intake and milk yield. Significant changes were also recorded in milk quality. Milk fat content was depressed by BG and MSH but increased by FB, while MS and FB increased milk protein content when compared with GS. The aim of the current study was to determine the effect of concentrate level on feed intake and milk production of Friesian cows offered a forage ration of either GS or mixtures of GS and either 330 g/kg forage DM of MS, FB or BG, or 750 g/kg forage DM of maize silage (MSH).