The broad-horned flour beetle, Gnatocerus cornutus (F.), was investigated for an aggregation pheromone. The male volatile collected with a Porapak Q column showed attractancy for both sexes, indicating male beetles produced aggregation pheromone(s), Purification of the volatile from 761,000 male-day-equivalents (MDE) by silica gel column chromatography yielded two different active fractions. The major pheromone (total of 12.3 mg; 1MDE = 16.2 ng) isolated with a 5% AgNO3-SiO2 column was identified as a (+)-acoradiene on the basis of NMR, MS, IR and optical rotation. This acoradiene was active at more than 0.16 ng per disk, showing attractancy at the same level as the crude male volatile. An unidentified minor pheromone was ten times less active than the major pheromone. (C) 1998 Elsevier Science Ltd. All rights reserved.