Abstract Fluorescently labelled NPY Y 1 receptor (Y 1 R) ligands were synthesized by connecting pyrylium and cyanine dyes with the argininamide-type Y 1 R antagonist core structure by linkers, covering a wide variety in length and chemical nature, attached to the guanidine group. The most promising fluorescent probes had Y 1 R affinities (radioligand binding) and antagonistic activities (calcium assay) in the one-to two-digit nanomolar ...