Neurobiology. In the article “A Rap guanine nucleotide exchange factor enriched highly in the basal ganglia” by Hiroaki Kawasaki, Gregory M. Springett, Shinichiro Toki, Juan J. Canales, Patricia Harlan, Justin P. Blumenstiel, Emy J. Chen, I. Amy Bany, Naoki Mochizuki, Amy Ashbacher, Michiyuki Matsuda, David E. Housman, and Ann M. Graybiel, which appeared in number 22, October 27, 1998, of Proc. Natl. Acad. Sci. USA (95, 13278–13283), due to a printer’s error, the gene CalDAG-GEFII was referred to incorrectly in three places: in the heading of the second paragraph of Materials and Methods, in the first line of the Abbreviations footnote, and in line 11 of the second paragraph on page 13282.