4-Imidazoline derivatives represented by the formula (I) and/or formula (II): ##STR1## wherein R.sup.1 represents C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.8 alkenyl, C.sub.3 -C.sub.8 alkynyl, C.sub.3 -C.sub.8 cycloalkyl, or optionally substituted aralkyl; R.sup.2 and R.sup.3 independently represent hydrogen, C.sub.3 -C.sub.20 alkyl, C.sub.3 -C.sub.20 alkenyl, C.sub.3 -C.sub.20 alkynyl, C.sub.3 -C.sub.20 alkoxy, C.sub.3 -C.sub.20 alkenyloxy, C.sub.3 -C.sub.20 alkynyloxy, C.sub.3 -C.sub.8 cyloalkyl, C.sub.1 -C.sub.10 alkylthio, or optionally substituted aralkyl or aralkyloxy; R.sup.4 represents C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.8 cycloalkyl, or optionally substituted aralkyl; provided that R.sup.2 and R.sup.3 cannot be hydrogen at the same time, and pharmaceutically acceptable salts thereof. A pharmaceutical formulation containing the compound is also provided.