A cell line derived from embryonic tissues of the European corn borer, Ostrinia nubilalis (UMC-OnE), was established in EX-CELL 401 medium containing 10% fetal bovine serum. The cells grew in suspension, and were mainly spherical in shape. The cell doubling times at the 17th and 79th passages were 56 and 36 h, respectively. DNA amplification fingerprinting showed that the DNA profile of the OnE cell line was different from that of the southwestern corn borer, Diatraea grandiosella (UMC-DgE), and that of the cotton bollworm, Helicoverpa zea (BCIRL-HZ-AM1). The OnE cell line was responsive to treatments of 20-hydroxyecdysone and the ecdysone agonists, methoxyfenozide (RH-2485) and tebufenozide (RH-5992). These compounds caused similar effects on the cells, which included cell clumping and decreased cell proliferation. The clumps were observed on the third day of incubation, and became larger after 7 d of incubation. After 168 h of incubation, methoxyfenozide and tebufenozide were 35 and 11 times more effective, respectively, in inhibiting proliferation of the OnE cells than was 20-hydroxyecdysone.