(1) The chat genus Oenanthe with eighteen species shows much polymorphism of color pattern in six species. (2) The variation is on the whole strictly discontinuous (e.g., black throat 'present' or 'absent'). It is, therefore, presumably controlled by a single gene, switch gene, or linked chromosome section. (3) The frequency of the two alleles shows much geographical variation which either forms a regular cline or is irregular. The frequency of one of the alleles reaches 100 per cent in parts of the geographical range of five of the six species. (4) Since recent genetic evidence indicates that the alleles involved in balanced polymorphism have different selective values, it seems probable that many subspecies and species characters that have heretofore been considered as 'neutral' actually differ in their selective values.