Enantiostructure-activity studies of chlorophenoxybutyric and propionic acids have provided evidence for the dissociation of serum cholesterol lowering and platelet antiaggregatory activities from the adverse chloride ion channel mediated myotonic effects of these compounds. R-(+) propionic and butyric acid enantiomers, unlike achiral clofibric acid and the S-(-) isomers, did not inhibit chloride conductance in rat extensor digitorum longus muscle fibers in vitro but, like clofibric acid and the S-(-) isomers, retained the serum cholesterol lowering activity in a cholesterol-fed rat model. Additionally, a stereoselective and greater inhibition was observed for the R-(+) isomers against adenosine diphosphate and arachidonic acid induced human platelet aggregation.