Researchers at the University of California have identified in insects that the membrane transporter, Ecdysone Importer (EcI), is involved in the cellular uptake of the primary steroid hormone ecdysone. Specifically after transport through Ecl, ecdysone’s active form (20-hydroxyecdysone or 20E and related ecdysteroids) enters its target cells and binds to the ecdysone receptor (EcR), which forms a heterodimer with another nuclear receptor and activates transcription of multiple genes involved in molting and metamorphosis. This new discovery of Ecl’s role counters the prevailing consensus that steroid hormones diffuse through cell membranes. This will enable the screening of new compounds that interact with Ecl. Such new compounds may be used for insect pest control. Fig. 1 membrane transporters (blue) guide steroid hormones (blue dots) into cells. This new discovery counters the conventionally held scientific consensus that steroid hormones passively diffuse through cell membranes. Fig. 2 EcI mutants (bottom) were not able to enter into metamorphosis when compared to the control (top).