The quantitative requirements of the Tribolium confusum larvae for magnesium, calcium, sodium, and potassium are reported. Magnesium and potassium are definitely essential for larval growth. Without these elements, the larvae do not survive long. Calcium appears essential for imaginal metamorphosis. In its absence, rapid dehydration of the pupae occurs and emergence of the adult is practically suppressed. The importance of sodium could not be demonstrated because the minute quantities already present in the basal diet appear sufficient to meet the requirements of this insect. The requirements of both sexes for these cations are of the same order of magnitude. Additions of these cations in excess of the optimum values are well tolerated.