An investigation was made of the influence of an environmental calcium concentration gradient on the storage of calcium spherules in Helisoma duryi eudiscus. A preliminary survey of adult snails revealed that the primary sites of calcium storage are the subepithelial connective tissues of the mantle-edge, pulmonary region, and foot. Snails were hatched and raised for 6 weeks in one of seven solutions of different calcium concentrations. These calcium chloride solutions contained the following concentrations of calcium: 1, 2, 4, 8, 16, 32, and 64 mg calcium/100 ml of demineralized water. It was found that a significantly higher number of calcium spherules are stored at both extremes of this concentration range, that is, in the 1, 32, and 64 mg calcium/100 ml solutions. The effects of the intermediate concentrations on calcium storage are not significantly different with respect to each other.