Fluorescence polarization of 1,6-Biphenyl-1,3,5-hexatriene (DPH) was used to evaluate the effects of chlorpromazine HCl on the range of the rotational mobility of bulk bilayer structure of the synaptosomal plasma membrane vesicles (SPMV) isolated from a bovine brain. In a dose-dependent manner, chlorpromazine·HCl increased the anisotropy (r), limiting anisotropy (r_∞) and order parameter (S) of DPH in the membranes. Cationic 1-[4-(trimethylammonio)-phenyl]6-phenylhexa-1,3,5-hexatriene (TMA-DPH) and anionic 3[p-(6-phenyl)-1,3,5-hexatrienyl]-phenylpropionic acid (PRO -DPH) were utilized to examine the range of transbilayer asymmetric rotational mobility of the neuronal membranes. The anisotropy (r) of TMA-DPH in the inner monolayer was 0.034 greater than the value of PRO-DPH in the outer monolayer of the membranes. Both cationic TMA-DPH and anionic PRO-DPH were also used to examine the transbilayer asymmetric effects of chlorpromazine·HCl on the range of rotational mobility of the membranes. Chlorpromazine·HCl have a decreasing effects on the rotational mobility of the bulk bilayer structures and have a greater decreasing effect on the mobility of the inner monolayer as compared to the outer monolayer of the membranes. It has been proven that chlorpromazine·HCI exhibit a selective rather than nonselective fluidizing effect within transbilayer domains of the SPMV.