We have shown that bone cells possess high-affinity binding sites for glucocorticoids, and that certain other steroids (progesterone, aldosterone, estrogen, cortexolone) are capable of competing for these binding sites. Our current and proposed work includes determining whether this competition is also seen in the effects of the glucocorticoids on protein synthesis. Binding studies will be extended to determine whether the bound glucocorticoid is transported into the nuclei. Studies on estrogen binding will be initiated. Other studies with bone cells are designed to correlate effects of hormones (PTH, calcitonin) on calcium transport with actions on intra-cellular metabolic events (lactate production, alkaline phosphatase activity). Effects of vitamin D metabolites and congeners on bone resorption will be studied; direct effects of these compounds on calcification will be sought.