This project is designed to elucidate the magnitude, and hopefully, something of the mechanisms and control of the ion fluxes to and from the skeleton. The studies principally involve (but are not limited to) calcium, inorganic phosphate, lactate and potassium. The model system employed principally (but not exclusively) is calvaria from adult mice. The influences of metabolic inhibitors, hormones, and physiological stresses are under investigation. Modified Ussing Chambers permit the evaluation of unidirectional fluxes across ectocranial and endocranial surfaces. By the use of selected water space markers, in some instances the gradients between bone fluid and surrounding medium can also be evaluated.