Amino acids were efficiently removed in vitro from blood plasma, or its saline equivalent, with a standard hemodialyzer (artificial kidney). The rate of dialysis, or clearance, of the smaller amino acids approached that of urea, while the larger amino acids were removed at a slightly slower rate. A generalized inverse correlation was found between amino acid molecular weights and their clearance rates. By increasing the standard "blood" flow rate and/or the dialysate flow rate, the efficiency of the artificial kidney in removing amino acids from simulated blood was significantly increased. In the absence of endogenous influx, hemodialysis is an effective means for removing the entire spectrum of amino acids from circulating blood or its saline equivalent. These findings have provocative implications for experimental therapy based upon nutritional deprivations involving amino acids or other vital circulating biochemical components that may be differentially required by normal and cancer cells.