The measurement of antibodies directed against the cholinergic receptor, produced by myasthenic patients, involves a radioimmunoassay. The use of human muscular nicotinic cholinergic receptor is highly recommended for this assay. However, difficulties in supplying and standardizing this reagent led us to consider its replacement by the homologous cholinergic receptor constitutively expressed by the human cell line TE671. TE671 cells were grown in mass cultures on microcarriers and acetylcholine receptors were solubilized using detergents. Replacement of human muscular receptor by cellular receptor in the radioimmunoassay assay was assessed by challenging these 2 antigens for numeric or diagnostic correlations. Using TE671 receptor, the correlations observed were good and, despite a slight decrease in the absolute values of the titers, about 90 p. 100 of the assays provided the same diagnostic accuracy. Some interfering proteins, perhaps immature acetylcholine receptor alpha subunits, could be expressed and could account for the slight decline in the antibody titers obtained using TE671 receptor. These interferences could be overcome by a further step of purification and concentration of the various receptor preparations. Finally, TE671 receptor could definitely replace human muscular receptor for screening and measuring myasthenic patients auto-antibodies.