Population Biology. In the article “Concordance of gene genealogies reveals reproductive isolation in the pathogenic fungus Coccidioides immitis” by Vassiliki Koufopanou, Austin Burt, and John W. Taylor, which appeared in number 10, May 13, 1997, of Proc. Natl. Acad. Sci. USA (94, 5478–5482), the authors wish to point out that further molecular analysis has revealed the following errors in three of the published sequences. For the dioxygenase locus, the genotypes of isolates CA3 and CA5 should read as TTATC instead of CCGCT, and for the orotidine decarboxylase locus the genotype of TX1 isolate should read as CAAGCCAA instead of CAGGTTAG (Table 1). These corrections do not change the main results and conclusion of the paper, that Coccidioides immitis is subdivided into two reproductively isolated taxa, one of which is centered in California. Indeed, they indicate greater divergence between the two taxa, as follows. All gene genealogies now include a branch separating the Californian from the non-Californian isolates, indicating a more complete sorting of alleles between the two groups than previously apparent, though the genealogies are no longer significantly different by the partition homogeneity test (P = 0.38; paup*4.0d61). The partition between Californian and non-Californian isolates is still highly significant (P = 0.002), and the two groups are separated by 17 instead of 8 fixed differences, distributed among all 5 loci. Significance tests from randomizations of the corrected data set with and without the partition are as before (see Fig. 3), still consistent with panmixia within each of the two taxa. The average pairwise divergence of isolates within the Californian and non-Californian groups is d_C = 1.26 × 10⁻³ (2.32 × 10⁻³) and d_NC = 1.80 × 10⁻³ (3.05 × 10⁻³), respectively (coding regions only; values in parentheses based on third-base positions only); the average pairwise divergence between groups is d_C-NC = 10.75 × 10⁻³ (25.09 × 10⁻³), 10-fold larger than the within-group values, and the estimated time the two taxa have been reproductively isolated is 11 Myr instead of 8 Myr. The authors wish to thank Mathew Fisher (University of California, Berkeley) for pointing out the errors and supplying the correct sequences.