Here, we report the characterization of a human cDNA coding for the recently published amino acid sequence of a calcium-binding S100 protein, S100A12 (CGRP, calgranulin C, CAAF1, p6). The exon/intron structure of the S100A12 gene is similar to most other S100 genes. It is composed of three exons which are divided by two introns of 900 bp and 400 bp. The protein is encoded by sequences in exons 2 and 3, with exon 2 coding for the N-terminal 45 amino acids and exon 3 coding for the C-terminal 46 amino acids. So far, ten S100 genes are known to be located on human chromosome 1q21 in a clustered organization. Hence, we investigated whether S100A11 (S100C, calgizzarin) and S100A12 are also localized in the S100 gene cluster. We found both genes within the cluster, with S100A11 being close to S100A10 and S100A12 between the genes S100A8 and S100A9. Therefore, the S100 gene cluster now is composed of 12 differentially expressed family members.