Iron plays an important role in redox and other enzymes, making it an essential micronutrient for all living organisms. Iron's role in photosynthesis and respiration has created interest in the study of iron metabolism, which has been well documented in terrestrial plants. Poor solubility of ferric iron limits the availability of iron to organisms. In addition, most iron is not found in the bioavailable free form, instead being found in complex with organic ligands. For this reason, low iron concentration often limits the growth of marine phytoplankton. This necessitated the evolution of specialized systems for the uptake and storage of iron. This purpose of this research was to investigate the uptake and storage of iron in two species of marine phytoplankton. Tetraselmis suecica is a green alga originally isolated off the coast of England that is of potential interest in biofuels research because of its high lipid content. Emiliania huxleyi is a ubiquitous species of coccolithophore found widely in temperate areas around the world. Because it forms vast blooms each year, the role of E. huxleyi on the earth's biogeochemistry has been studied, particularly its impact on the carbon cycle. Because both of these organisms reach a density of over 10⁶ cells per mL in 12 days, they are ideal organisms for laboratory research. Additionally, both species can be grown axenically or in symbiosis with associated microbes. Iron uptake in both species was investigated by pretreatment of cultures under ironlimited conditions followed by inoculation with radioactive ⁵⁵Fe to monitor iron uptake. Uptake studies indicated that iron uptake is an active transport process in both Tetraselmis suecica and E. huxleyi. The use of metabolic inhibitors and iron chelators indicate the use of reductive-oxidative pathways for iron uptake by T. suecica and possibly by E. huxleyi. Assaying for iron reduction using C₁₈ sep-pak columns in conjunction with the iron(II) chelator ferrozine show that T. suecica, and possibly E. huxleyi, exhibit iron(III) chelate reduction that is induced under iron-limited conditions.