Neurobiology. In the article “Alleviation of x-irradiation-based deficit in memory-based learning by d-amphetamine: Suggestions for attention deficit-hyperactivity disorder” by D. A. Highfield, D. Hu, and A. Amsel, which appeared in number 10, May 12, 1998, of Proc. Natl. Acad. Sci. USA (95, 5785–5788), the following correction should be noted. The last sentence in the paragraph entitled “Neuroanatomical Procedures” on page 5786 should read: “Only those rats in the x-irradiation conditions that showed about a 75% [not “at least an 80%”] decrease in dentate gyrus granule cells (as compared with sham irradiated) were used in the analysis.”