An experiment on twenty-four trios of rats was undertaken to determine the effect of excressive calcium nutrition, especially in adult life, on growth, longevity and calcification of the tissues, such as occurs in many of the soft tissues during senescence. Twenty-four rats were carried from weaning to death on a diet containing about 1% of calcium. Another group of the same size subsisted on a diet containing 1% of calcium during the growing period and then only 0.7% for the remainder of their lives. A third group was raised on a 0.6% calcium level and then on a 0.22% level. The diets were otherwise satisfactory especially with reference to vitamin D and phosphorus. The rate of growth was not appreciably affected by the different dietary regimes, though among the female rats the more liberal calcium diet was associated with a greater degree of adult “growth,” probably consisting mainly of fat deposition. The data on longevity do not reveal any significant diet effects among either male or female rats. The great variability in age at death among rats on the same diet, represented by a standard deviation of 185 days, testifies to the difficulty of establishing the statistical significance of imposed experimental conditions in longevity studies. A slight tendency for somewhat greater calcification of the soft tissues, especially of the muscles, on the highest calcium regime studied, is suggested by the data presented, though complications induced by the terminal illness render interpretation of these differences difficult.