Calcium plays an important role in various myopathies. We report on an animal model with increased plasma creatine kinase (CK) resulting from hypocalcemia that will provide clues for studying human hypocalcemic myopathy. Male Wistar rats were pair-fed either a control or a calcium- and vitamin D₃-deficient diet for 1, 2, 3, 4, or 5-6 weeks after weaning (3 weeks old). In the deficient diet-fed rats, plasma creatine kinase was increased and was accompanied by marked hypocalcemia. The omission of calcium and vitamin D₃ from the diet for 1 or 2 weeks was enough to cause increased plasma creatine kinase; the creatine kinase ratio of deficient diet-fed rats to controls was 4.84 (1,777 IU L⁻¹/367 IU L⁻¹), and the calcium ion ratio was 0.41 (1.8 mg dL⁻¹/4.4 mg dL⁻¹) after 2 weeks. These values returned to control levels on treatment of the rats with the control diet and 1⍺-OH-vitamin D₃ for 1 week.