The invention relates to a method for increasing the efficiency of surfactants as well as to a method for suppressing lamellar mesophases in microemulsions. According to the invention, block copolymers having a water-soluble block A and a water-insoluble part B are admixed to the surfactants. The use of these substances as additives can considerably increase the efficiency of the surfactants. Moreover, the addition of the block copolymers suppresses the formation of undesired lamellar mesophases in microemulsions.