The present invention provides a novel steroid inducible expression system in a non-mammalian host cell (e.g., fungal) that is independent of metabolic and developmental regulation. The human estrogen receptor gene expressed in Aspergillus, under a constitutive promoter, was shown to be functional. A construct containing a promoter from Aspergillus, synthetic sequence containing the estrogen receptor biding sites (EREs) and a reporter gene was expressed in response to a hormone derivative inducer. In the absence of the inducer, the promoter is silent and depending on the type of construct and inducer concentration the expression level can be modulated from moderate to very strong.