In order to clarify the mechanism underlying the integration of multiple sensory stimuli in the neuronal network, the chemotactic responses of the nematode Caenorhabditis elegans to simultaneous presentation of water-soluble sodium acetate and an odorant diacetyl, which were sensed by different sensory neurons and integrated by common interneurons, were examined. The fraction of animals that gathered at the 0.7 M sodium acetate location was greater than that at the 0.1% diacetyl location in the presence of both attractants (p<0.05), although the chemotaxis indexes for 0.7 M sodium acetate and 0.1% diacetyl were similar in the presence of a single attractant. On the other hand, the fraction of animals that gathered at the 0.02% diacetyl location was greater than that at the 0.1 M sodium acetate location in the presence of both attractants (p<0.05), although the chemotaxis indexes for 0.02% diacetyl and 0.1 M sodium acetate were similar in the presence of a single attractant. These results suggest the existence of excitatory and/or inhibitory connections in the neuronal circuit for attractant selection, and that the efficacy of these connections may change according to the concentrations of both attractants. [Jpn J Physiol 55 Suppl:S157 (2005)]