Responses of single olfactory cells on the antennal club ofIps pini have been recorded electrophysiologically. The majority of cells were strongly activated by either/or of the two behavior-modifying chemicals, the aggregation pheromone ipsdienol and the aggregation inhibitor ipsenol. Simultaneous stimulation with these terpence alcohols showed that ipsenol had no inhibitory effect on the receptor responses to ipsdienol. It appears that the behavioral inhibition by ipsenol on the attraction of ipsdienol results from central integration of the information from separate receptor cells rather than blockage at the peripheral receptors.