Two sets of hormonal peptides are synthesized which are super agonists of the luteinizing hormone releasing hormone (LHRH). Chronic administration results in the inhibition of LHRH which is responsible for stimulating cell growth in the testes. One peptide has the D(dextro)-form of a monoheterocyclic amino acid in position six (D-3-pyridyl-alanine) while the other peptide has a bi-heterocyclic amino acid in that same position (.beta.-(3-quinolyl)-D-.alpha.-alanine. Both peptides are less metabolically reactive than those in the prior art and yet both peptides are significantly more potent than LHRH itself.