Modifications of standard instrumental neutron activation analysis procedures have produced quantitative results for REE, Th, and U contents of the biogenically precipitated apatite of conodonts and ichthyoliths. These results are in agreement with isotopic studies of four of the samples. Apatite of modern fish debris apparently concentrates REE during early diagenesis in the same proportions as seawater, and therefore carries a signature of the oceanic REE pattern, suggesting the same relationship between fossil apatite and ancient seas. REE patterns of conodont samples from Cambrian through Triassic times show significant secular variations. Further, these data show that REE vary among depositional...