FIELD : chemistry. SUBSTANCE : invention relates to PYY compounds having the amino acid at the position corresponding to position 30 in hPYY(1-36), substituted by tryptophan, and its derivatives with a modifying group attached at the position corresponding to position 7 in hPYY(1-36). In the method, the compounds are selective Y2 receptor agonists. Also the invention relates to pharmaceutical compositions containing such PYY compounds and pharmaceutically acceptable excipients, as well as the medical use of PYY compounds for the treatment and/or prevention of diabetes mellitus and related diseases. EFFECT : proposed are selective PYY compounds and their applications. 9 cl, 10 tbl, 45 ex