Acknowledgments. The US. Public Health Service and the Intramural Fund of the University of California, Riverside, provided the financial support for this study. 2 We thank Dr. M. Rappoldt of Philips-Duphar (Weesp, the Netherlands) for generous gifts of vitamin Dz and dihydrotachysterolz. AM acknowledges the Spanish Ministry of Education and Science for postdoctoral support. Dr. Milton L. Hammond provided extensive and helpful input during ...