Three feeding trials with growing lambs were carried out in order to evaluate the protein value of some common protein feeds in the supplementation of wheat straw in complete pelleted diets. The protein feeds were: soya bean meal (SBM), sunflower cake (SFC), coconut cake (CNC), brewers yeast (BY), meat meal (MM), fish meal (FM), blood meal (BM) and a commercial product based on blood meal integrated with lysine and methionine and protected with calcium soaps to escape the rumen. The results confirm that wheat straw is a potentially good source of energy, provided it is associated with a slowly degradable protein source. SBM was the best feed of plant origin and comparable with feeds of animal origin. SFC was the worst feed in this respect. When a protected protein replaces a fraction of the protein of SBM, the crude protein level of the diet can be lowered from 16-18 per cent down to 13 per cent on the DM basis. The statistical 'response surface analysis' was a unique tool to show the best combinations between ingredients.