The invention relates to new .alpha.-arylethylpiperazine of the formula ##STR1## wherein Z represents 0 or S; n' represents 1 or 2; R.sup.2 represents a hydrogen atom or a methyl group; W, Ar.sup.1 and Ar.sup.2 represent various substituents as defined herein; or non-toxic pharmaceutically acceptable salt, individual optical isomer, or individual diastereoisomer thereof, which are useful as neurokinin receptor antagonists (NK.sub.1 antagonists). It also relates to processes for their preparation and use in methods for treatment of asthma and/or allergic rhinitis.
