The binding affinities of agonists at heteromeric nicotinic receptors composed of rat alpha2, alpha3 and alpha4 subunits in combination with beta2 or beta4 subunits were examined in stably transfected HEK 293 cells. In most cases, the affinities of agonists were higher at receptors composed of an alpha subunit in combination with the beta2 subunit than the beta4 subunit, and in some cases this difference was quite large (>250 times), suggesting the possibility of developing subtype-selective ligands and therapeutically useful drugs.