N- methyl -N--acyl glucamine in an aqueous solution of a surfactant containing one or two or more anionic surfactants from the group of alkyl ether sulfates and alkyl sulfates are suitable for thickening, its When, N- methyl -N--acyl glucamine is, C 12 - acyl, C 14 - C 18 acyl groups or unsaturated - a N- methyl -N--acyl glucamine containing an acyl group of at least 60 wt% are contained, and simultaneously, N- methyl -N--acyl glucamine containing the fatty acid residue of the