A detergent base which is obtainable from the reaction of an ethylenically unsaturated sulfonic acid or carboxylic acid or anhydride thereof with a nonionic surfactant of the formulaR.sub.1 --O-(alkylene-O).sub.n.sbsb.1 --R.sub.2 (1)in whichR.sub.1 is C.sub.8 -C.sub.22 alkyl or C.sub.8 -C.sub.18 alkenyl;R.sub.2 is hydrogen, C.sub.1 -C.sub.4 alkyl, a cycloaliphatic radical having at least 6 C atoms or benzyl; andn.sub.1 is a number from 1 to 60;and if appropriate with sugar derivatives.The detergent base has a good calcium-dispersing power, is very stable to electrolytes and heat and has an excellent washing action and anti-redeposition properties. It is therefore suitable for the preparation of powder and liquid detergents.