A petroleum ether extract of Piper guineense male roots showed insecticidal activity when tested against Musca domestica. Gas chromatography of the extract yielded four active fractions, one of which was a pure component which was identified by spectral and chemical methods as pellitorine (N-isobutyl-2E,4E-decadienamide). The root extract lost about half of its insecticidal potency during passage down the GLC column, and much of the residual activity was due to the presence of pellitorine. It was concluded that GLC facilitates the isolation of active components in a pure form, but causes some insecticidal components of the root extract to be lost.