Black pepper, Piper nigrum L. (Piperaceae), has insecticidal properties and could potentially be utilized as an alternative to synthetic insecticides. Piperine extracted from P. nigrum has a biphasic effect upon cytochrome P450 monooxygenase activity with an initial suppression followed by induction. In this study, an ethyl acetate extract of P. nigrum seeds was tested for insecticidal activity toward adult Musca domestica and Drosophila melanogaster. The effect of this same P. nigrum extract upon differential gene expression in D. melanogaster was investigated using cDNA microarray analysis of 7380 genes. Treatment of D. melanogaster with P. nigrum extract led to a greater than 2-fold upregulation of transcription of the cytochrome P450 phase I metabolism genes Cyp 6a8, Cyp 9b2, and Cyp 12d1 as well as the glutathione-S-transferase phase II metabolism gene Gst-S1. These data suggests a complex effect of P. nigrum upon toxin metabolism.