[en] Investigations were undertaken to elucidate the mode of transepithelial transport of potentially toxic metal ions across the gastrointestinal tract, with primary attention given to cadmium, zinc, and arsenic. In addition, the toxic effects of cadmium on the metabolism of vitamin D and calcium have been investigated in some detail. Several approaches have been taken, including studies on the localization of heavy metals in the intestinal mucosa, the effects of cadmium on various parameters of calcium metabolism, the modes of intestinal absorption of cadmium, arsenate, and zinc, and the interactions of heavy metals with each other and with calcium, phosphorus, and vitamin D. Details of these experiments are attached in the Comprehensive Progress Report