Abstract: Novel vasotocin derivatives having an inhibitory effect on uterine contractions, pharmaceutical compositions containing these derivatives, and the use thereof in the therapeutical treatment of excessive muscle contractions in the uterus and described. The derivatives differ from vasotocin in that the structure of the original hormone has been modified at positions 1, 2 and, optionally, 4 and/or 8. The vasotocin derivatives thus have the formula ##STR1## wherein Mpa is a 3-mercaptopropionoyl residue (--S--CH.sub.2 --CH.sub.2 --CO--);A is the peptide residue of L- or D-tyrosine-O-ethyl ether (in other words, 4-ethoxy-L or D-phenyl alanine, i.e.

Abstract: New oxytocin derivatives having an inhibitory effect on uterine contractions, pharmaceutical compositions containing the oxytocin derivatives, and use of the derivatives in the production of medicines are described. The derivatives are 1-deamino-(2-O-alkyltyrosine)-oxytocin of the formula ##STR1## wherein Mpa is a 3-mercaptopropionyl residue and X is an alkyl group having 2-4 carbon atoms, preferably an ethyl group. Apart from their inhibitory effect on vasopressin and oxytocin induced uterine contractions, the new oxytocin derivatives are capable of inhibiting the spontaneous contraction pattern of the uterus.