Isoelectric protein concentrates (IPC) were prepared from one buckwheat (Fagopyrum esculentum) and five Amaranthus genotypes. Their effect on the mixing properties of a wheat flour was studied. Mixograph and dynamic oscillatory measurements showed significant increases in dough strength with the addition of 2 and 4% IPC, correlated to the water-insoluble fraction level of the IPC. The same IPCs were used at 2% level to supplement a wheat flour in making Chinese dry noodles. Measurable changes in both the raw and cooked noodle color were observed, and the change caused by addition of buckwheat IPC was substantial. Some of the IPCs caused an increase in cooking loss and only one caused an increase in weight, while increase in volume of the cooked noodles was not significantly affected. The changes in the rheological properties of cooked noodles due to addition of IPCs were measured. Overall, their effects were favorable, but the changes were statistically significant in only a few cases. The substantial dough-strengthening effect of the IPCs was hence not effectively translated into improved cooked noodle quality, and possible reasons for this are discussed.