The epithelial cell line from Chironomus tentans, derived from embryos grows as multicellular spheroids. The individual cells are connected regularly by cell junctions typical for insect epithelia. The enzyme pattern is characteristic for epidermal tissue. Ecdysteroids induce morphological and physiological changes, which remind to the first steps of imaginal disc evagination of holometabolous insects. The hormonal regulation of genes involved in this morphogenetic reaction varies in a gene specific way. Besides moulting hormone, the essential growth factor insulin and the neurotransmitter acetylcholine seem to be involved in the control of cell proliferation and cell differentiation. After 15 years of continuous culture the cell line is still remarkably stable. Meanwhile a number of stable resistant subclones were isolated with different defects in the hormone signaling pathway. Therefore this cell line represents a powerfull tool to elucidate the molecular mechanism of ecdysteroid hormone action.