By utilizing novel stable isotope dilution techniques recently developed in our laboratory, we will trace deuterium labeled ß-carotene in intrinsically labeled spirulina, which is harvested from a hydroponic system. In the mean time, we will track 13C10 labeled vitamin A in humans. In this way we will determine absorption of ß-carotene from spirulina matrix and the conversion of the spirulina ß-Carotene to retinol. This will enable us quantitatively determine the vitamin A equivalence of spirulina.