The effects of diet and intranephronic calculosis on bone modeling parameters and parathyroid volumes in the rat were studied. Bone chemical analyses and histomorphometric evaluation indicated that a modified AIN diet, containing minimal required levels of calcium, phosphorus and magnesium, was not nutritionally adequate. Although the mineral content of the modified AIN diet barely met the demands for normal bone modeling, both the AIN-76TM and modified AIN diet caused intranephronic calculosis. Nephrolithiasis was not observed in rats fed a natural-product diet. After 10 days, the medullary cavity size and the index of resorption were slightly greater in rats fed the calculogenic diets, but these effects were not evident at 9 weeks. A slight but highly significant difference in the bone magnesium content was observed between rats fed the semipurified and natural-product diets. At 9 weeks, the parathyroid volumes were slightly increased in rats fed the AIN-76 diet compared to rats fed the natural-product diet. It was concluded that differences in dietary content that promote or inhibit intranephronic calculosis do not alter intestinal absorption as much as they influence molecular and cellular events occurring after absorption.