The aggregation pheromone of Pityogenes hopkinsi Swaine was identified; it is a three-component mixture, comprising chalcogran, cis-verbenol, and ethyl dodecanoate. Ethyl dodecanoate is new as a bark beetle pheromone component. Chemical analyses (GC–MS) were made on hindgut extracts from unmated and mated males and mated females collected in the field during colonization of Pinus strobus L. (Pinaceae). Aerations from the naturally colonized logs were also analyzed to quantify the released amounts of the pheromone components, a necessary preliminary step to making up biologically relevant doses for field bioassay. Beetles reared from infested host material in the laboratory were introduced into logs of P. strobus, and the production and release of pheromone components in relation to attack phase and "mating status" were described. In general, unmated males increased their production of chalcogran and ethyl dodecanoate until females were admitted, after which production ceased. A field subtractive bioassay showed that chalcogran was the key pheromone component, synergized by different compounds for the two sexes. Females exhibited their strongest response to a mixture of chalcogran and ethyl dodecanoate, whereas cis-verbenol was the synergist for male response. Male-produced 1-hexanol had an inhibitory effect on male attraction to the aggregation-pheromone blend.