Abstract A modern automated technique has been used to re-evaluate the older standard classic methods for studying the amino acid composition of human albumin. Previous published data have been derived from pooled samples that included persons of unknown clinical status. In this study normal values were determined for albumin derived from healthy volunteers and purified by electrophoresis on polyacrylamide gel. Patients with rheumatoid arthritis were similarly evaluated. No differences attributable to age were found. Albumin from women contained 20% more threonine than did albumin from men. Patients with rheumatoid arthritis had more phenylalanine and less lysine in their albumin than did normal persons. No such differences in composition of structural proteins have been previously demonstrated. It is unlikely that the substitution of one amino acid for another in molecules of this size could arise by chance during protein synthesis.