Aqueous infusions of decayed paper birch,Betula papyrifera(Marsh), are shown to contain an oviposition attractant for the tree-hole mosquitoAedes triseriatus(Say) in laboratory experiments. The attractive material is proved to be volatile and soluble in pentane.p-Cresol is shown to be an active component of this extract. Further experiments demonstrate that contact of ovipositing mosquitoes withp-cresol odor alone suffices to induce significantly increased oviposition. Trapping experiments show thatp-cresol solutions attract significantly more mosquitoes, both male and female, than does distilled water alone.