The concentrations of magnesium and calcium in the serum and urine and their rates of clearance were determined in cattle with renal tubular dysplasia, an autosomal recessive hereditary disease associated with a deletion of the paracellin-1 gene in Japanese Black cattle. There were no significant differences in the serum or urine magnesium concentrations between normal cattle and cattle which were heterozygous or homozygous for the condition. Serum calcium concentrations tended to be lower in the homozygous cattle, and the serum creatinine and urea nitrogen concentrations were significantly higher in the homozygous cattle. The ratio of magnesium:creatinine and the fractional excretion of magnesium were higher in cattle with the disease than in normal cattle. There were no significant differences in urine calcium concentration, the calcium:creatinine ratio, and fractional excretion of calcium between normal cattle and cattle which were homozygous or heterozygous for the condition. The creatinine clearance was significantly lower in the homozygous cattle than in normal cattle. The clearance, excretion rate, reabsorption rate and reabsorption rate:clearance ratio of magnesium in cattle with renal tubular dysplasia were significantly lower than in normal cattle. The clearance rate and reabsorption rate of calcium were also significantly lower in the affected cattle, but the excretion rate and reabsorption rate:clearance of calcium were not different between the normal cattle and the cattle homozygous for the condition. In cattle with the condition the rate of reabsorption of magnesium by the kidneys was low, but the rate of reabsorption of calcium was normal.