ABSTRACT - The transport of C-amino acids into human erythrocytes and into erythrocytes which had been frozen and thawed was studied experimentally. The relative rates of uptake were found to be (in decreasing order): phenylalanine, leucine, alanine, trythophan, and glycine. Freezing (using gycerol as the cryoprotective additive) and thawing had no significant effect on either the magnitude of the rate constants or on the order of the above relative rates of amino acid uptake into erythrocytes suspended in isotonic TRIS-HCl buffer