A microchip array encompassing probes for 14,010 genes of Drosophila melanogaster was used to analyze the effect of juvenile hormone (JH) on genome-wide gene expression. JH is a member of a group of insect hormones involved in regulating larval development and adult reproductive processes. Total RNA was isolated from Drosophila S2 cells after 4 hours treatment with 250 ng/ml (10R) JH III or 250 ng/ml methyl linoleate. A collection of 32 known or putative genes demonstrated a significant change with JH III treatment (r > 2.0, P <or= 0.005). Of these, the abundance of 13 transcripts was significantly increased and 19 decreased. The expression of a subset of these loci was analyzed by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Three loci that exhibited constant expression in the presence and absence of JH III (RP49 [FBgn0002626], FBgn0023529, and FBgn0034354) were evaluated and found to be reliable invariant reference transcripts for real-time RT-qPCR analysis using BestKeeper and geNorm software. Increased expression in presence of JH III was confirmed by real-time RTqPCR analysis. However, only one of five loci that exhibited reduced expression on microarrays could be confirmed as significantly reduced (P <or= 0.05). Among the confirmed JH III up-regulated genes were two loci of unknown function (FBgn0040887 and FBgn0037057) and Epac, an exchange protein directly activated by cyclic AMP, a guanine nucleotide exchange factor for Rap1 small GTPase.