The surface behavior of neurotransmitters, their agonists and antagonists on a gold electrode/phosphate buffer solution was studied by specular reflection measurement. There was adsorption of the following neurotransmitters: ~/-aminobutyric acid, glycine, ~-alanine, dopamine, norepinephrine, epinephrine, acetylcholine, glutamic acid, and aspartic acid in the potential range of -200 to 200 mV vs. the point of zero charge. The potential profiles of adsorption between inhibitory and excitatory neurotransmitters were noted to differ. Their antagonists were adsorbed onto the electrode more strongly than the neurotransmitters. The adsorption potential profile provides clarification of the electrostatic interactions between the receptor site and neurotransmitter or related drugs.