NEW MATERIAL: A carboxylic acid derivative of formula I (wherein Ar1 is unsubstituted or substituted aryl; Ar2 is unsubstituted or substituted arylene; R1 is H, an aliphatic group or an aryl-aliphatic group; R2 is an aliphatic group or an aryl-aliphatic group; R3 is H, lower alkyl or lower alkanoyl; and Z is a divalent aliphatic group) and a salt thereof.

EXAMPLE: {0-[(2,6-Dichlorophenyl)amino]phenyl}aceto-N-methylhydroxamic acid.

USE: Useful as pharmaceuticals, for example for anti-inflammatory or anti-allergic.

PREPARATION: A compound of formula II is reacted with a compound of formula III, or the protecting group P1 in the compound of formula IV or a salt thereof is converted into hydrogen, or a compound of formula V is reacted with a compound of formula VI (wherein X1 is reactive esterified hydroxy) to obtain a compound of formula I.