ABSTRACTPotato tubers had 1.67% N/dry matter. Nitrogen was distributed in all anatomical regions of the tuber. Of the total N content, 43% was dialyzable‐N and 32.9% true protein‐N. The protein, by solubility fractionation, provided 67% albumin, 23% globulin, 1.4% prolamin and 9% glutelins. As revealed by sodium dodecyl sulfate electrophoresis (SDS‐PAGE), the albumin had two major protein species, one of 45 × 103, the second of 12–25 × 103daltons. Prolamin and glutelins contained protein bands coinciding in molecular weight with those of albumin and globulin.Protein hydrolysis with 4 N methanesulfonic acid was superior to that of 6 N HCL. Amino acid composition of proteins was determined by ion‐exchange column chromatography. Some minor losses in protein composition of potatoes occurred during