Among the calcium-binding proteins from chicken gizzard smooth muscle, smooth muscle calcium-binding protein 11 (SMCaBP 11), which is an EF-hand type calcium-binding protein, can prevent Ca2+ dependent histamine release from permeabilized rat peritoneal mast cells. This activity appears to be specific since other calcium-binding proteins (CaBPs), including h-calcimedin, l-calcimedin, calmodulin and S100, had no inhibitory action. Approximately 40% of the histamine release was inhibited by SMCaBP 11 at 48 nM and the half-maximal inhibition occurred at 20 nM. Immunological techniques revealed that permeabilized mast cells elicited by Ca2+ also released actin into the medium, but not tubulin. The addition of SMCaBP 11 prevented the secretion of actin from the mast cells, though the distribution of F-actin was only slightly affected. These findings suggest that SMCaBP 11 may modulate Ca2+ and actin-mediated exocytosis from permeabilized mast cells.