A new substituted metaaminophenol of formula (I): ##STR1## wherein Z represents a monohydroxylated or polyhydroxylated hydrocarbon radical of 1 to 6 carbon atoms or an aminoalkyl radical of the formula: ##STR2## wherein n is an integer from 1 to 6 and R.sub.1 and R.sub.2, which are identical or different, represent a hydrogen atom or an alkyl or hydroxyalkyl radical of 1 to 6 carbon atoms or an acyl radical of 1 to 4 carbon atoms, and R represents a hydrogen atom, an alkyl radical or monohydroxyalkyl or polyhydroxyalkyl, monocarbamylalkyl, dicarbamylalkyl, aminoalkyl, acyl, carbalkoxy, carbamyl or monoalkylcarbamyl radical, the abovementioned alkyl radicals containing 1 to 6 carbon atoms, or an acid salt thereof with the proviso that if R represents a hydrogen atom, Z cannot represent --CH.sub.2 CH.sub.2 OH is disclosed, together with a process for their preparation, hair-dyeing compositions containing them and a hair-dyeing process.