4-(Nitrophenyl)-1,2,3,4-tetrahydropyridines of the formula ##STR1## in which R.sub.1 and R.sub.2 are identical or different and each represent hydrogen, phenyl or a straight-chain or branched alkyl radical which is optionally substituted by halogen or alkoxy,R.sub.3 represents a straight-chain or branched alkyl radical which is optionally substituted by alkoxy, halogen, alkylamino or aryl,X represents a single bond, an oxygen atom, a sulphur atom or the NH group andY denotes either the nitrile group or the radical ##STR2## wherein X' corresponds to the definition of X and can either be identical to X or different from X, andR.sub.4 corresponds to the definition of R.sub.3 and can be either identical to R.sub.3 or different from R.sub.3,or physiologically acceptable salts thereof, which are active on the circulation system, for example as vasodilators.