NEW MATERIAL: A compd. represented by formula I (wherein Ar is 4-halophenyl, Ar' is 1,3- or 1,4-phenylene, Y is (E)-CH=CH- and R1 and R2 are each H or 1-4C alkyl) and its salt.

EXAMPLE: (E)-N-{3-[3-(4-fluoroephenoxy)phenyl]-1(R,S)-methyl-2-propen-1-yl)-N- hydroxyurea.

USE: This new material is used as a 5-lipoxygenase inhibitor and an antioxidant and useful for treating and preventing an allergy state, tumorigenesis, platelet aggregation related state, inflammation or atherosclerosis.

PROCESS: A chiral compd. represented by the formula, R3NHOH (R3 is a group represented by formula II) is reacted with group I cyanate (e.g. potassium cyanate) in a solvent such as THF in the presence of an acid to obtain the compd. represented by formula I.