Ryanodine receptors (RyR) are Ca(2+)-induced Ca(2+) release channels located on the endoplasmic reticulum, and consist of three isoforms, termed RyR1-3. We examined their expression in developing mouse brains by in situ hybridization. During the embryonic stage, RyR1 mRNA levels were highest in the rostral cortical plate, whereas RyR3 mRNA was most prominent in the caudal cortical plate and hippocampus. Initially, low levels of RyR2 mRNA were distributed in the diencephalon and brainstem. However, from postnatal day 7 onward, RyR2 mRNA became the major isoform in many brain regions, while RyR1 mRNA became prominent in the dentate gyrus and Purkinje cell layer. Postnatal down-regulation in the caudal cerebral cortex restricted RyR3 mRNA expression to the hippocampus, particularly the CA1 region. Therefore, RyR expression undergoes dynamic changes during the early postnatal period, when neurons are undergoing structural and functional differentiation.