Vasomotoricity in veins is largely controlled by the sympathetic nervous system. Norepinephrine and acetylcholine modulate the vasoconstrictor effect mediated by alpha-adrenergic receptors. Our objective was to study the role of local vasomotoricity in venous thrombosis, and particularly to determine some of the factors regulating it. Although no attempt has been described until now, polyclonal and monoclonal antibodies against L-dihydroxyphenylalanine, acetylcholine, and dopamine were administered in an experimental model of venous thrombosis. In view of the rather high specific antibody recognition for each compound, the presence of endogenous epitopes of L-dopa-like molecules and acetylcholine-like molecules in the circulation can be postulated. The results of this study may open an important new approach in the treatment of vascular diseases.