Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) is a monomeric, multifunctional serine/threonine protein kinase that is expressed in subanatomic regions of the central and peripheral nervous system, T lymphocytes, and male germ cells. It is frequently localized to the nucleus, where it serves as a mediator of Ca(2+)-dependent gene expression. Although CaMKIV expression in the adult rat central nervous system and thymus has been described, little is known about the embryonic expression of murine CaMKIV. Here we report a thorough embryonic expression study of CaMKIV mRNA from embryonic day 9.5 through postnatal day 1. Expression patterns during embryonic development are significantly different from those of adults, suggesting specific roles for CaMKIV during development. Regions of high CaMKIV mRNA expression include thymic and bone cartilage primordia as well as specific cranial nerve ganglia (trigeminal, vestibulocochlear, and glossopharyngeal), thalamus, and dorsal root ganglia. This pattern of expression is chronologically consistent with periods of extensive cellular differentiation, proliferation, or neuronal survival selection and shows a predilection for neural crest-derived cells. These trends, along with recent studies in the CaMKIV null mouse, suggest that CaMKIV may play an important physiological role in cellular differentiation during embryogenesis.