The extract of left (LVC) and right (RVC) turtle visual cortex locally applied to the surface of turtle visual cortex inhibited the orthodromic evoked potentials (EP; fast negative component N1). The inhibition was partially (70-90%) prevented by opiate antagonist naloxone. LVC-extract proved to be a more potent inhibitor of the left cortex EP, whereas RVC-extract was slightly more effective when applied to the right cortex. The extracts of the left and right hemispheres of rat brain, but not the extract of the whole brain, applied subarachnoidally into the caudal portion of a transected spinal cord at the T7-T9 level, induce postural asymmetry of hind limbs in rats. The extract of the left hemisphere predominantly induce flexion of the left leg, and the extract of the right hemisphere induce flexion of the right leg. The factors of the right brain hemisphere able to induce postural asymmetry (PAFs) have been studied in detail. PAFs are thermostable compounds inactivated by trypsin and papain. Naloxone significantly reduces the number of asymmetries. HPLC analysis of the rat and pig right hemisphere extract has revealed two PAFs which differ from enkephalins, endorphins and dynorphin. The activity of PAFs in rat pituitary is significantly lower than in the brain. These findings suggest the existence of side-specific mechanism for selective neurohormonal regulation of neuronal activity and other processes in the left and right halves of the brain which involve lateralized factors of turtle visual cortex and PAFs.