The cDNA of human and murine S100A13 was first identified by screening expressed sequence tag data bases. The human S100A13 was shown to neighbor S100A1 on chromosome 1q21. Expression of S100A13 mRNA has so far been detected in skeletal muscle, heart, kidney, pancreas, ovary, spleen, and small intestine. S100A13 seems to function in exocytosis, since it is one of the targets of two antiallergic drugs, amlexanox and cromolyn, which inhibit degranulation of mast cells. Recently, association of S100A13 with the fibroblast growth factor 1 (FGF-1)/p40 synaptotagmin-1 (p40Syn-1) aggregate was shown, and amlexanox is able to repress this release. These findings suggest that S100A13 might be involved in the regulation of FGF-1 and p40Syn-1 release in response to heat shock. Another possibility might be that S100A13 is secreted together with the FGF-1/p40Syn-1 aggregate.