ABSTRACT.Two odour receptor cells were physiologically identified within male antennal hair sensillae of the gypsy moth, Lymantria dispar L, and the nun moth, L. monacha L. In the gypsy moth, one cell responded to (+)‐disparlure, while a neighbouring cell responded to (‐)‐disparlure. In the nun moth both cells responded to (+)‐disparlure. The lack of sensitivity to (‐)‐disparlure in the nun moth was corroborated by electroantennogram (EAG) recordings, which indicated no affinity to this enantiomer. Single cell responses of male gypsy moth to different concentrations of the synthetic enantiomers of disparlure were then compared to responses elicited by hexane extracts of female glands of both species. The gypsy moth's extracts stimulated almost exclusively the receptor cell specialized for (+)‐disparlure, while both cells were simultaneously stimulated by the extracts of the nun moths. From the response characteristic of the cells it is estimated that pheromone production of the nun moth is about 10% (+) and 90% (‐)‐disparlure, and that of the gypsy moth is almost 100% (+)‐disparlure. Stimulation of the antenna of each species by female gland extracts of both species did not indicate the presence of receptors for other hexane elutable pheromone component