Chemistry. In the article “Virtual combinatorial libraries: Dynamic generation of molecular and supramolecular diversity by self-assembly,” by Ivan Huc and Jean-Marie Lehn, which appeared in number 6, March 18, 1997, of Proc. Natl. Acad. Sci. USA (94, 2106–2110), the following changes should be noted. On page 2106, the first line in the second paragraph should read “Dynamic combinatorial chemistry is a conceptually different… .” On page 2110, the fourth line in the second paragraph should read “… the assembly-forming connections scheme of brain function (34)… .”