Twelve novel bis- or tris(macrocyclic) compounds have been designed as models for cation-conducting channels that function in phospholipid bilayer vesicle membranes. In general, the channel model systems have the structure "sidearm-crown-spacer-crown-spacer-crown-sidearm", although certain features have been altered from compound to compound to assess the structure-activity relationship. Two additional compounds have been prepared exclusively as controls. The ionophores have been incorporated into the membranes either by warming the compound with the preformed vesicle or by incorporation during vesicle formation. The two methods gave identical results within experimental error. Cation flux was assessed by two different analytical methods. In one case, the fluorescent dye pyranine was encapsulated within vesicles containing ionophore. Proton transport was then monitored by changes in dye fluorescence with time following an acid pulse. Ionophoretic activity far most of the compounds was studied using a dynamic NMR method in which the flux rate of Na-23(+) through the bilayer was monitored. All NMR studies were done in conjunction with gramicidin as a control to minimize experimental variations from run to run. Several of the synthetic ionophores showed cation conduction of as much as 40% of the activity of gramicidin. Apparently, small structural changes significantly altered flux rates and two known carriers closely related to the channel formers failed to exhibit measurable transport under comparable conditions.