Previous treatment of color variation in practically all species of bats has been quite arbitrary, with no consideration of molt and subsequent changes in color. The present paper attempts to interpret certain heretofore undescribed aspects of color variation in Tadarida brasiliensis mexicana (Saussure) and Myotis velifer incautus (J. A. Allen), necessarily describing the time and sequence of molting. Indications are that once each year adults of both species molt into a fresh, dark-colored coat, and this coat eventually fades or bleaches to a markedly lighter color.