YM-44781 free acid is a non-peptide neuropeptide receptor antagonist with efficient NK(2) and NK(1) receptor antagonist activity. YM-44781 exhibits significant binding affinity on the NK(2) receptor (p K i = 9.94) and also on the NK(1) receptor Higher binding affinity (p K i = 9.09). In addition, YM-44781 also showed significant inhibitory effects on bladder contraction induced by selective NK(1) receptor agonists.