There is provided a compound of formula I,
##STR00001##
wherein R.sup.1a, R.sup.1b, X, Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4,
Z.sub.1, Z.sub.2, R.sup.2 and R.sup.3 have meanings given in the
description, and pharmaceutically-acceptable salts thereof, which
compounds are useful as selective agonists of the AT2 receptor, and thus,
in particular, in the treatment of inter alia gastrointestinal
conditions, such as dyspepsia, IBS and MOF, and cardiovascular disorders.