Isocyanato compounds with capped, isocyanate-reactive groups are those of the formula I ##STR1## where R.sup.1 and R.sup.2 are hydrogen, C.sub.1 -C.sub.10 -alkyl, C.sub.6 -C.sub.10 -aryl or C.sub.7 -C.sub.10 -aralkyl or together form C.sub.3 -C.sub.10 -alkanediyl,X and Y are --O--, --S-- or ##STR2## where R.sup.4 is hydrogen, C.sub.1 -C.sub.20 -alkyl which is uninterrupted or interrupted by oxygen atoms in ether function, or is C.sub.6 -C.sub.10 -aryl or C.sub.7 -C.sub.10 -aralkyl,R.sup.3 is C.sub.1 -C.sub.10 -alkanediyl which together with --X--CR.sup.1 R.sup.2 --Y-- forms a 4-7-membered ring,in which either one hydrogen in R.sup.3 or the radical R.sup.4 in ##STR3## is replaced by an allophanate group R.sup.Ia ##STR4## in which R.sup.5 is a divalent aliphatic, alicyclic, araliphatic or aromatic C.sub.2 -C.sub.20 hydrocarbon unit,R.sup.6 is a single bond or a divalent aliphatic, alicyclic, araliphatic or aromatic C.sub.1 -C.sub.20 hydrocarbon unit or a mono- or poly(C.sub.2 -C.sub.4 -alkylene oxide) unit, andR.sup.7 is a carbamoyl radical ##STR5## or a biuret group R.sup.Ib ##STR6## in which one R.sup.8 is hydrogen and the other is as defined for R.sup.7 or a biuret group R.sup.Ic ##STR7## in which one R.sup.9 is as defined for R.sup.7 and the other is as defined for R.sup.1or a thioallophanate group R.sup.Id ##STR8##