Triazole derivatives represented by formula (IIA), and salts and prodrug thereof, wherein R.sup.1 represents C.sub.1-6 alkoxy(C.sub.1-6)alkyl, C.sub.2-6 alkenyl, C.sub.2-6 alkynyl, C.sub.3-7 cycloalkyl, C.sub.3-7 cycloalkyl(C.sub.1-6)alkyl, aryl, aryl(C.sub.1-6)alkyl, aryloxy(C.sub.1-6)alkyl, aryl(C.sub.2-6)alkenyl, aryl(C.sub.2-6)alkynyl, C.sub.3-7 heterocycloalkyl(C.sub.1-6)alkyl, heteroaryl, heteroaryl(C.sub.1-6)alkyl, heteroaryl(C2-6)alkenyl or heteroaryl(C.sub.2-6)alkynyl, any of which groups may be optionally substituted; are selective agonist of 5-HT.sub.1 -like receptors and are therefore useful in the treatment of clinical conditions, in particular migraine and associated disorders, for which a selective agonist of these receptors is indicated. ##STR1##