Four members of the nuclear factor of activated T cells (NFAT) family (NFATC1, NFATC2, NFATC3, and NFATC4) are Ca(2+)-regulated transcription factors that regulate several processes in vertebrates, including the development and function of the immune, cardiovascular, musculoskeletal, and nervous systems. Here we describe the structures and alternative splicing of the human and mouse NFAT genes, including novel splice variants for NFATC1, NFATC2, NFATC3, and NFATC4, and show the expression of different NFAT mRNAs in various mouse and human tissues and brain regions by RT-PCR. Our results show that alternatively spliced NFAT mRNAs are expressed differentially and could contribute to the diversity of functions of the NFAT proteins. Since NFAT family members are Ca(2+)-regulated and have critical roles in neuronal gene transcription in response to electrical activity, we describe the expression of NFATC1, NFATC2, NFATC3, and NFATC4 mRNAs in the adult mouse brain and in the adult human hippocampus using in situ hybridization and show that all NFAT mRNAs are expressed in the neurons of the mouse brain with specific patterns for each NFAT.