This dataset characterizes the elemental and macromolecular content in cultures of two marine diatoms (Thalassiosira pseudonana, Thalassiosira weissflogii) and two marine prasinophytes (Ostreococcus tauri, Micromonas sp.). For each of these four species, the total cellular content of carbon, nitrogen, phosphorus, protein, carbohydrate, lipid, RNA, DNA, phospholipid, and pigments are shown at several sampling points ranging from nitrogen-replete to nitrogen-starved growth conditions.