chifish is a 32-bit Windows/DOS program evaluating divergence at multiple gene loci. It tests the hypothesis of no difference at any locus both by means of Pearson's traditional chi-square and by using Fisher's method of combining P values obtained by Fisher's exact test. Input data are read from a file formatted for genepop. Commonly used population genetics software do not perform chi-square tests, and the simultaneous application of both techniques aids in situations where poor power of the ‘exact approach’ may prevent detection of true differentiation (e.g. few populations and few alleles per locus).