Microalgal species vary in their sensitivity to the triazine herbicides, including cyanazine. The current investigation was carried out to examine the uptake and the effects of cyanazine on Chl (a) content, growth rate, EC50, and protein and amino acid contents of two different algal species; namely Scenedesmus obliqutis (green alga) and Anabaena flos-aquae (blue green alga). With regard to the differential sensitivity, the present findings revealed that S. obliqutis is more sensitive to the inhibitory effects of cyanazine compared to A. flos-aquae (EC50 = 26 vs. 113 mu g/L. respectively). Additionally, the lowest applied concentrations of the tested herbicide increased the Chl (a) content of both algal cultures as well as its rate of uptake. (C) 2009 Elsevier B.V. All rights reserved.