Analogues of PYY differing from native human PYY by substitution of Ser23 with Ala23, Glu23, Lys23, Gln23 or AIB23. Further optional features include substitutions at further positions, loss of the Tyr1 residue of native human PYY and amidation of the C-terminus. Suitable for use as pharmaceuticals for treating and preventing disorders, in particular diabetes and obesity.