A nomsotoplc receptor based assay IS developed which IS centered upon the u-toxm-bmdmg mcotmlc acetylchohne receptor and fluorescem labeled cu-bungarotoxm The assay method IS based on sequential saturation of the receptor by unlabeled and fluorophore labeled hgands, followed by separation of the free from the bound label by cenfrlfugatlon Subsequently, the free concentration IS determined by use of a flow mJectlon system Unlabeled hgands investigated include both the agonist and antagonist types that bmd to the receptor a-subumts, I e, a-bungarotoxm, carbamylchohne, decamethomum, gallamme, d-tubocurarme, pancuromum, and hexamethomum The effectiveness of the proposed method IS illustrated by Scatchard analysis, Hill plot of the labeled hgand, and displacement curves for unlabeled hgands Keywords Acetylchohne receptor, Chohnerglc hgands Utlhzatlon of isolated receptors m the characterization and screening of pharmacologically active substances has become an important tool m blomedlcal research Radio-isotope receptor based bmdmg assay 1s currently one of the most commonly used methods and has become a routme technique m drug discovery and development Nomsotoplc assay development has recently attracted great attention due to the health hazard and special disposal requirements of radio-labeled compounds [l-4] Because of the fact that receptors exist m extremely low concentration m tissues (pmol to nmol/g protein), the labels must have good detection senatlvlty, as well as high affinity and speclflclty for the recep-