Mathematical models are presented to describe the relationship between nitrogen consumption, biomass growth, and carotenoid production by the microalgae Dunaliella tertiolecta BE 003 grown under nitrogen-limited and nonlimited conditions. The nitrogen uptake was modeled by an n-order nitrogen-catalyzed reaction. Three different expressions were proposed for the biomass-specific growth rate. Carotenoid production was fitted using the Luedeking-Piret equation. The nitrogen-catalyzed expression proved to be adequate to model nitrogen uptake by D. tertiolecta over a wide range of nitrogen concentrations. Biomass expression must be improved to describe the cessation of growth when nitrogen is still available in the cultures. The Luedeking-Piret expression successfully modeled the carotenoid production.