A rational use of native cyanobacteria for diverse biotechnology purposes requires the study of the local abiotic factors that could potentially affect their normal growth. The present study deals with the herbicide bentazon (0.75, 1.5 and 2 mM)-induced changes in lipid profile and antioxidative defense system parameters related to oxidative stress in the rice field cyanobacterium strain Nostoc muscorum UTAD_N213 grown under laboratory conditions for 72-h. Results indicate that the 72-h exposure of the strain to increasing bentazon concentrations caused: (1) a decrease of the polyunsaturated fatty acids (FAs); (2) an increase of the saturated FAs; and (3) a decrease of the unsaturation index. The activities of all of the antioxidant enzymes except for glutathione reductase showed a significant increase upon bentazon exposure in a time- and concentration-dependent manner. When compared to untreated controls, the oxidized glutathione content increased by 42.79 and 119% with 0.75, 1.5 and 2 mM bentazon, respectively, whereas the reduced to oxidized glutathione ratio decreased by 32, 50 and 61%, respectively. The accumulation of proline in cells after herbicide exposure might prevent bentazon-induced production of reactive oxygen species and functions as a protecting agent against oxidative damage. (C) 2011 Elsevier Ltd. All rights reserved.