Samples of the following 14 genera of algae were collected from various geographical or geological areas during the period from April to November 1965 and subjected to mineral determinations; Anabaena, Aphanizomenon, Chara, Cladophora, Euglena, Hydrodictyon, Lyngbya, Micro cystis, Mougeotia, NiteUa, Oedogonium, Pithophora, Rhizoclonium, and Spirogyra. There was considerable variation in the levels of most elements, both within and between genera. Phytoplankton algae had low metal ion contents and high carbon, nitrogen, and phosphorous concentrations. Nonplankton algae generally contained more metallic ions and less carbon, nitrogen, and phosphorous. There was a marked mean accumulation of one or more elements above the usual levels by several genera as follows: nitrogen, cyanophycean genera and Euglena; phosphorus, cyanophycean genera; sulfur, Aphanizomenon, Hydrodictyon, and Pithophora; potassium, Hydrodictyon and Nitella; calcium, Chara and Pithophora; magnesium, Chara; sodium, Spirogyra; boron, Pithophora and Lyngbya. Both Chara and Pithophora were extremely rich in most bases and low in carbon when compared to other genera. Almost all genera contained relatively high levels of copper, iron, manganese and zinc. Emission spectrographic analyses of Chara, Euglena, Microcystis, Pithophora, Rhizoclonium and Spirogyra revealed the presence of substantial quantities of aluminum, barium, cobalt, molybdenum, silicon, and strontium. These compositional data indicate that algae play an important role in the mineral dynamics of aquatic ecosystems.