A water dispersible, modified polyurethane which resists microbial attack, exhibits superior efficiency in thickening aqueous compositions and imparts improved leveling, is the reaction product of:

a) a polyisocyanate;
b) from 0.10 to 10.00 moles per mole of polyisocyanate of a polyether polyol;
c) from 0.015 to 3.400 moles per mole of polyisocyanate, of a modifying agent having the formula
wherein R represents a group containing from 0 to 10 carbon atoms, X is a group containing at least one active hydrogen moiety selected from primary amino, secondary amino, carboxyl and mixturesthereof, Y is a group containing at least one active hydrogen moiety selected from primary amino, secondary amino, carboxyl, hydroxyl, mercapto and mixtures thereof, the sum of (x + y) is an integer greater than 1, and X is at least 1; and
d) capping agent which is reactive with the reaction product of (a) the polyisocyanate, (b) the polyether polyol and the (c) modifying agent, and which is present in an amount sufficient to cap the said reaction product.