We report the isolation of a clone encoding calmodulin from a rat brain cDNA library; genomic clones were also isolated and partially characterized. The derived amino acid sequence has 100% homology to the published mammalian protein sequences. In rat, we identify two major RNA species of approximately 2.2 and 0.75 kb in length by RNA blot analysis. Furthermore, the mRNA is highly enriched in brain tissue, compared to liver or kidney. A variant (GATAAA) of the putative poly(A) addition signal is observed at the 3' end of one of the mRNA species.