Abstract: Substituted 6-R-1,3,4-thiadiazin-2-amines of the following general formula: ##STR1## wherein Ar is phenyl or phenyl optionally substituted with one or more chloro, bromo atoms, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 alkyl groups; R.sup.1 and R.sup.2 are each independently hydrogen atom or C.sub.1 -C.sub.4 alkyl moiety; and R.sup.3 and R.sup.4 are independently selected from C.sub.1 -C.sub.4 alkyl groups and pharmaceutically acceptable salts thereof, the use of them as anaesthetics, cardiovascular and hypometabolic agents and pharmaceutical compositions containing them.