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Calponin is a smooth muscle specific, actin-, tropomyosin- and calmodulin-binding protein thought to be involved in regulation of actomyosin as well as the regulation or modulation of contraction (1). Calponin binds filamentous actin (F-actin) through two distinct sites ABS1 and ABS2, with an affinity in the low micromolar range (2) Immunoreactivity for calponin, along with alpha-smooth muscle actin and smooth muscle myosin heavy chains, confirms the known neoplastic myoepithelial component of adenoid cystic carcinomas and epithelial-myoepithelial carcinomas. The consistently positive staining pattern in adenoid cystic carcinomas may be diagnostically useful in discriminating histologically similar but consistently negative polymorphous low-grade adenocarcinomas (3).