Abstract: The invention relates to a new process for the preparation of nitraminodiaryl sulfoxide derivatives of the formula (I), ##STR1## wherein R and R.sup.1 represent hydrogen or alkyl having from 1 to 6 carbon atoms, andR.sup.2 is hydrogen, halogen, alkyl having from 1 to 6 carbon atoms, alkoxy having from 1 to 6 carbon atoms, or phenyl or thiophenyl both optionally substituted by one or more identical or different halogen(s) and/or nitro group(s).The compounds of formula (I) are pharmaceutically active, and are particularly useful in the veterinary therapy as anthelmintics. In addition they show pesticidal, particularly acaricidal, fungicidal and herbicidal properties. The invention relates also to pharmaceutical and pesticidal compositions containing as active ingredient compounds of formula (I).The compounds of formula (I), in which the substituents are as defined, with the proviso that if R.sup.2 is hydrogen and the substituent --N(R,R.sup.1) is in para-position related to the sulfoxide group, R and R.sup.