Fluoride contents of planktonic foraminiferal calcite show a strong relation to the depth habitat of a given species. Shallow-water species such as Globigerinoides ruber and Globigerinoides sacculifer have fluoride contents more than three times those of deeper dwelling species such as Globorotalia truncatulinoides and Globorotalia menardii. This correspondence between chemistry and life habitat is consistent from glacial to interglacial samples and from tropical to mid-latitude samples. Oxygen isotopic composition and minor element contents (Sr, Mg) all have a positive covariance with F content, suggesting that F content is controlled by temperature and/or growth rate. Species-specific vital effects may also have an influence on F content. These initial data suggest that habitat differences among species and possibly temperature variations within species may be determined by the F content of foraminiferal calcite in well-preserved materials. Fluoride contents of older Cenozoic planktonic foraminiferal species may provide a useful test of assumed life habitats.