The present invention provides a novel N-hydroxyurea compound of chemical formula (I) wherein R.sup.1 and R.sup.2 are each independently hydrogen or C.sub.1 -C.sub.4 alkyl; Ar is phenyl or mono-, di- or trisubstituted phenyl; A is a valence bond or a C.sub.1 -C.sub.6 alkylene chain, optionally having one double bond or one triple bond in the chain, and optionally having one or more C.sub.1 -C.sub.4 alkyl groups attached to the chain: X is oxygen or sulfur, n is an integer of 3 to 6; M is hydrogen, pharmaceutically acceptable cation or a metabolically cleavable group: and X and A may be attached at any available position on the ring. These compounds are useful for treatment or alleviation of inflammatory diseases, allergy and cardiovascular diseases in mammals and as the active ingredient in pharmaceutical compositions for treating such conditions.