Male C57BL/6J mice ranging in age from 50 to 1186 days were used to measure total calcium and calmodulin concentrations. The increase in calcium between 0 and 1,000 days of age was 260% for kidney, followed by brain (189%), heart (173.5%), lung (106.5%) and liver (78.5%). Calcium in femur declined by 28.2%. The calmodulin content of liver increased with ageing. Both liver and kidney calmodulin concentrations declined early in life followed by ageing-related increases. Brain, lung and heart calmodulin concentrations did not change significantly with ageing. We conclude that changes in calcium homeostasis are not reflected in calmodulin changes. The loss of calcium in bone is consistent with the occurrence of osteoporosis in ageing C57 mice.