Two types of neurons exhibiting various reactions to application of antibodies against S100 protein in the washing solution were revealed in the nervous system of Helix lucorum snails. After treatment with antibodies against S100 protein the frequency of action potential generation decreased in spontaneously active B1, B3, B17, and PPa6 cells, but increased in B4 and B6 cells. The effect of antibodies against S100 was less pronounced in the solution of potentiated antibodies against this protein. After pre-exposure of ganglia in the solution of potentiated water the effect of antibodies against S100 protein decreased to a lesser extent. No significant changes were revealed in the membrane resting potential of cells. Combination treatment with antibodies and potentiated antibodies against S100 protein increased the threshold of action potential generation in B1 and B17 cells. Our results indicate that potentiated antibodies against S100 protein specifically modulate the activity of nerve cells.