It is unclear whether burn blister fluid is beneficial or deleterious to the healing of the underlying wound. We investigated the calcium binding protein calmodulin in human burn blister fluid and its role in the mitogenicity of this fluid in the culture of human keratinocytes, fibroblasts, and mouse 3T3 fibroblasts. Calmodulin levels in blister fluid were three times greater than in serum (p < 0.005), whereas epidermal growth factor and platelet-derived growth factor concentrations were significantly lower (p < 0.001). Calmodulin in blister fluid was biochemically identified after affinity chromatography, Western blotting, and immunostaining with a monoclonal antibody. Inhibiting calmodulin with either an antagonist or antibody to calmodulin reduced the mitogenic activity of blister fluid in three cell types by 26% to 80%. These in vitro studies suggest that burn blister fluid may promote wound healing, and locally released calmodulin contributes to this effect. In appropriate cases it may be beneficial to leave burn blisters intact.