Synergism was demonstrated by injn. into adult milkweed bugs. In 3 proportions of joint application, observed mortality was far larger than expected. Other tests combining the highest concn. of one material and the lowest of another, and intermediate doses of both in a dosage series, also showed strong evidence of synergism. Finally, survivors of injn. with one material were injected at intervals of 24 hours with the other, the results of which indicated that nicotine "conditions" insects for a higher mortality from pyrethrum.