Floristic survey of flagellate green algae (Chlorophyceae and Prasinophyceae) from four water bodies in the state of Rio de Janeiro, southeast Brazil. Samples were collected bimonthly from September 1988 to August 1991. Thirty-five taxa of which 31 in Chlorophyceae (24 Chlamydomonadales and seven Volvocales) and four in Prasinophyceae (Polyblepharidales) were identified. Twenty-three taxa are new records for Brazil and 31 are registered for the first time for Rio de Janeiro State. On basis of cell shape, location of the nucleus and degree of longitudinal striations on the chloroplast surface a new combination, Vitreochlamys lefevrei (Bourr.) Menezes & C. Bicudo, is proposed. Integrating studies among morphological analysis on natural/cultured material and characterizing of reproduction/life cycle as well the correlating between the occurrence of the species and environmental conditions are needed in order to better knowledge the degree of phenotypic plasticity within the members of the flagellate green algae in the country.