Dr. Milch made some interesting comments about alcaptonuria which, however, are controversial. No attempts were made in my paper, which was a general review article on amino acid metabolism, to explore the various facets of this problem. First: It would seem to me, that with the demonstration of a defect in a single enzyme system that alcaptonuria is a single disease, not a "syndrome." Alcaptonuric individuals may differ in their clinical manifestations, but the common denominator is the biochemical defect.