Hydroxamic acid esters of the formula ##STR1## in which R.sup.1 is an optionally substituted alkyl, cycloalkyl, aryl or aralkyl radical andR.sup.2 is an alkyl, alkenyl or alkinyl radical, orR.sup.1 and R.sup.2 together are an alkylene bridge with 2 to 4 carbon atoms,one of the radicals R.sup.3 and R.sup.4 is ##STR2## while the other is an alkyl, alkenyl, alkinyl, halogenoalkenyl or alkoxyalkyl radical, andX is O or S,which possess pesticidal properties. Intermediates therefor wherein one of N--OR.sup.3 and N--OR.sup.4 is N--OH or a carbonyl group are also new.