The synthesis and resolution of (+/-)-3-methoxycyproheptadine [(+/-)-4] are described. As a peripheral serotonin antagonist, (+/-)-4 was found to be one-half as potent as cyproheptadine (1b). The peripheral anticholinergic and antihistaminic activities as well as the orexigenic property of (+/-)-4 are less than those of 1b. A further comparison of the enantiomers (+)-4 and (-)-4 shows that all of the anticholinergic activity of (+/-)-4 resides solely in the dextrorotatory enantiomer, (+)-4, while the antiserotonin activity, which is similar to that of 1b, resides in the levorotatory enantiomer, (-)-4. Antihistaminic and orexigenic activity also resides in (-)-4 but these properties are reduced compared to those of 1b.