this paper deals with a qualitative analysis of the Class Euglenophyceae from Negro river, Uruguay South America. Samples were collected between November 1994 and February 1995. A total of 54 taxa were recorded, 3 belonging to Lepocinclis, 3 to Phacus, 26 to Strombomonas and 22 to Trachelomonas. On the basis of these observations we propose one new variety S. scabra var. piriformis and a new forma S. urceolata var. elegans fo. americana. Twenty three taxa have been examined by means of scanning electron microscopy. The high species richness was registered at Paso Ramirez (PR). Some parameters physical-chemicals are also given.