The invention comprises compounds of the formula <FORM:1077974/C2/1> wherein each of R1 and R2 represents a hydrogen atom or a C1- 4 alkyl, phenyl-C1- 4 alkyl, C1- 4 hydroxyalkyl, C1- 4 alkoxy-C1- 4 alkyl, di-(C1- 4 alkyl)-amino-C1- 4 alkyl or C2- 5 alkoxy-carbonyl-C1- 4 alkyl group, and each of R3 and R4 represents a hydrogen or halogen atom or a C1- 4 alkyl or C1- 4 alkoxy group, non-toxic acid addition salts thereof, and their preparation by (a) reacting 1-phenyl-4-oxo-1,2,3,4-tetrahydro quinolines of the formula <FORM:1077974/C2/2> with hydroxylamine to form the corresponding 1 - phenyl - 4 hydroximino - 1,2,3,4 - tetrahydroquinolines, reducing these hydroximino compounds to the corresponding 4-amino compounds (Formula I, R1=R2=H), and, if desired, substituting one or both of the hydrogen atoms in the 4-amino group by the radicals listed above for R1 and R2, or (b) by reacting compounds of the Formula II with compounds of the formula NH2-R1 in which R1 has the meaning given above except for hydrogen, to form the corresponding 4-imino compounds, reducing these imino compounds to form the corresponding 4-mono-substituted-amino compounds (Formula I, R2=H), and, if desired, replacing the hydrogen atom of the mono-substituted-amino group by a radical listed above for R2. The free bases can be converted into the corresponding salts with non-toxic mineral or organic acids. 1 - Phenyl - 4 - oxo - 1,2,3,4 - tetrahydroquinolines of the Formula II are prepared by cyclization of the corresponding b -diphenylamino-propionic acids which are themselves prepared by reaction of the corresponding diphenylamines with b -propiolactone. b - (4,41 - Diethyl - diphenylamino) - propionic acid is characterized by its S-benzyl-isothiouronium salt. 1 - Phenyl - 4 - (31 - hydroxy-propionamido) - 1,2,3,4 - tetrahydro - quinoline is characterized by its phenyl isocyanate derivative.