Method for production of deuterated beta -carotene for the bioavailability studies of vitamin A has been developed using Spirulina platensis in culture. Suspension cultures of Spirulina in heavy water (99.4% D2O) medium produced maximum biomass and beta -carotene in 28 to 30 days. Of the total carotenoids, lutein constituted 30 to 35% while beta -carotene was about 24%. MS showed that 60 to 65% H atoms in beta -carotene were deuterated. 100% replacement of H atom with deuterium was achieved by preventing exchange with atmospheric moisture. The medium could be used in several cycles for metabolic labelling of carotenoids whereby the cost of production is reduced.