Novel 5-HT.sub.3 receptor antagonist compounds having following formula (I) ##STR1## wherein n is 1, 2 or 3;each of R, R.sub.1 and R.sub.2, which may be the same or different, is hydrogen, halogen, hydroxy, cyano, C.sub.1 -C.sub.6 alkyl, CF.sub.3, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, formyl, C.sub.2 -C.sub.6 alkanoyl, carboxy, C.sub.1 -C.sub.6 alkoxy-carbonyl, nitro, --N (R.sub.4 R.sub.5) in which each of R.sub.4 and R.sub.5 independently is hydrogen, C.sub.1 -C.sub.6 alkyl, formyl or C.sub.2 -C.sub.6 alkanoyl; or a (R.sub.6 R.sub.7) N--SO.sub.2 group, in which each of R.sub.6 and R.sub.7 independently is hydrogen or C.sub.1 -C.sub.6 alkyl;R.sub.3 is an imidazolyl group of formula ##STR2## wherein each of R.sub.8 and R.sub.10 which may be the same or different is hydrogen or C.sub.1 -C.sub.6 alkyl, R.sub.9 is hydrogen, C.sub.1 -C.sub.6 alkyl or a nitrogen protecting group; and the pharmaceutically acceptable salts thereof, are disclosed.