A distinct age dependence was observed in the occurrence of the gamma-carboxyglutamic acid containing proteins obtained from kidney cortex, liver and femoral bone. In the femoral bone, a stepped increase was seen when comparing animals 60, 350 and 700 days old. In the liver and mainly in the kidney cortex there was no change during the first year of life, but a distinct increase in the gamma-carboxyglutamate containing proteins was seen between day 350 and 700. It was also established that the increased level of gamma-carboxyglutamate at least in kidney cortex is due to a more intense carboxylation reaction in older animals as increased incorporation of labelled bicarbonate was observed in the microsomal fraction. In accordance with our previous results the occurrence of the carboxyglutamic acid containing proteins was shown to be vitamin D dependent; in vitamin D deprived animals supplemented with this vitamin the reappearance of gamma-carboxylate is more distinct in situations where higher levels of gamma-carboxyglutamic acid occur physiologically.