The synthesis and pharmacological characterization of dithiobisacetylcholine and dithiobis-N,N-dimethyl-4-acetylpiperazinium (two oxidizing analogs of acetylcholine), as well as those of their reduced counterparts, are described. Both the oxidizing and reducing analogs stimulate nicotinic receptors in the chick retina and block the binding of 125I-labeled neuronal bungarotoxin to retinal homogenates (IC50 values of 2 x 10(-6) to 6 x 10(-5) M). Both oxidizing compounds reverse the physiological effects of reduction by dithiothreitol on nicotinic function in intact chick retina, when applied for 2 sec (EC50 values of about 10(-5) M). This effect is selective, insofar as neither agent alters the effects of dithiothreitol treatment on receptors for N-methyl-D-aspartate. Reoxidation takes place at the disulfide located near the nicotinic receptor agonist binding site, inasmuch as reoxidation by these agents prevents affinity alkylation by bromoacetylcholine, and occupation by the competitive antagonist d-tubocurarine prevents reoxidation. Unlike thiocholine, a weak agonist with a free sulfhydryl that, paradoxically, is reported to oxidize nicotinic receptors in electroplax, the reduced forms, mercaptoacetylcholine and N,N-dimethylamino-4-mercaptoacetylpiperazinium, have no direct redox effects on retinal receptors, but they do protect the receptors against reduction by dithiothreitol.