Polyorganopolysiloxane/polyoxyalkylene block compolymers suitable for use as stabilizers in making soft polyurethane foams, of the formula[R.sup.1 Si(OSiR.sub.2).sub.n ].sub.m Z.sub.m-1 (OR.sup.2).sub.m+2in whichR is an optionally halogen-substituted alkyl group with up to 4 C atoms,R.sup.1 is the substituent R or a phenyl radical,R.sup.2 is an aliphatic, optionally unsaturated radical with up to 18 C atoms or a group of the formulaR.sup.3 (OCH.sub.2 CH.sub.2).sub.x (OCH.sub.2 CH).sub.y -,Z is the difunctional unit --O-- or ##STR1## R.sup.3 is a hydrocarbon radical with up to 4C atoms, R.sup.4 each independently is a hydrogen atom or R.sup.3,n is from 3 to 30,m is from 1 to 15,x is from 0 to 68,y is from 0 to 52,x+y is from 1 to 68, andP is from 2 to 12,are produced by reacting an organopolysiloxane of the formulaR.sup.1 Si(OSiR.sub.2).sub.n U.sub.3-a-b Cl.sub.a W.sub.bin whichU is a radical of a lower monobasic carboxylic acid with up to 4 C atoms,W is a radical of a fluorinated alkanesulphonic acid,a.ltoreq.1, andb.ltoreq.0,5,with a mixture of R.sup.2 OH and H-Z-H, in the presence of a base in an organic solvent, the relative proportion of the reactants being determined by the value of m.