POPULATION BIOLOGY. In the article “Origin of a new Phytophthora pathogen through interspecific hybridization” by C. M. Brasier, D. E. L. Cooke, and J. M. Duncan, which appeared in number 10, May 11, 1999, of Proc. Natl. Acad. Sci. USA 96, 5878–5883, the authors wish to note that all of the Genbank accession numbers were missing one digit. The correct numbers are as follows: AF139366, AF139367, AF139368, AF139369, and AF139370.