Adult male Neoclytus mucronatus mucronatus (F.) (Coleoptera: Cerambycidae: Cerambycinae) were observed to display behaviors identical to calling behaviors of the congener N. acuminatus acuminatus F., males of which produce an aggregation pheromone. Odors collected from male N. m. mucronatus contained one major male-specific compound, identified as (R)-3-hydroxyhexan-2-one. Bioassays determined that both sexes were weakly attracted to racemic 3-hydroxy-2-hexanone. Further field trials determined that enantiomerically enriched (R)-3-hydroxyhexan-2-one (94% ee) attracted more beetles of both sexes than did the racemic blend. This aggregation pheromone is produced by glands that discharge through pores lying within shallow cuticular depressions in the pronotum of male N. m. mucronatus.