Abstract   Arabidopsis plants were transformed with a multi-gene construct for expression of the polyhydroxybutyrate (PHB) biosynthetic pathway containing a gene switch that can be activated by commercially available non-steroidal ecdysone analogs approved for use on some crops as pesticides. T₁ progeny of transgenic Arabidopsis plants were isolated and screened for PHB production in the presence of ecdysone analogs. T₂ progeny derived from selected T₁ lines were subjected to further analysis by comparing PHB production levels prior to treatment with inducing agent and 21 days after initiation of induction. Significant PHB production was delayed in many of the engineered plants until after induction. PHB levels of up to 14.3% PHB per unit dry weight were observed in young leaves harvested from engineered T₂ plants after applications of the commercial ecdysone analog Mimic^®. PHB in older leaves reached levels of up to 7% PHB per unit dry weight. This study represents a first step towards engineering a chemically inducible gene switch for PHB production in plants using inducing agents that are approved for field use.