Six gemini surfactants of general formulas (CH3)(2)RN+(CH2)(n)N+R(CH3)(2)center dot 2Br(-)(I) (R = C12H25, n = 2, 8, 12, or C16H33, n = 6), and (CH3)(2)RN+(CH2)(2)(OCH2CH2)(m)N+R(CH3)(2)center dot 2Br(-)(R = C12H25, m = 1 or C16H33, m = 1) were synthesized and used as surface-active compds. in glyphosate formulations for controlling cornflower (Centaurea cyanus L.), winter wheat (Triticum aestivum L.) and rye brome (Bromus secalinus L.) under greenhouse conditions. The I (n = 2, 8, 1 2) surfactants were most active in improving herbicide activity of N-phosphonylmethyl-glycine.