Two spontaneous firing giant neurones (TAN, tonically oscillating neurone and PON, periodically oscillating neurone) were identified in the subesophageal ganglia of Achatina fulica Ferussac. Effects of vaso-active peptides (substance P, physalaemin, eledoisin-related substance, neurotensin, bradykinin (B.K.), Lys-B.K., Met-Lys-B.K., angiotensin (A.G.) Ⅰ, A.G. Ⅱ, hypertensin, A.G. Ⅲ) were examined on the excitability of these two neurones. Physalaemin showed the excitatory effect on the TAN excitability. This effect was due to depolarizing the TAN neuromembrane. The critical concentration (in bath application) was about 5x10(-5)g/ml. All of amino acids, of which physalaemin consists, were ineffective on the TAN excitability. The other mentioned peptides than physalaemin were ineffective on the same neuromembrane. All of peptides examined in the present work were ineffective on the PON excitability. Effects of vaso-active peptides are considered to be selective in the neuronal level.