CULTURED mammalian cells are finding increasing use as a basis for conducting physiological and biochemical investigation outside the organism. Insect cell lines have originated from primary explants of embryonic tissue or tissues from larval and pupal stages of the donor. Cells from primary explants of embryonic tissue from the fruit fly, Drosophila melanogaster; the mosquito, Aedes aegypti; leaf hoppers, Agallia constricta and A. quadripunctata; and cockroaches, Periplaneta americana and Blabera fusca, continued to multiply and were subcultured1-4. Primary cultures of larval tissues from, the silkworm, Bombyx mori; the rice stem borer, Chilo suppressalis; and mosquitoes, Aedes aegypti, A. albopictus and Anopheles stephensi, were subcultured and developed into cell lines5-11. Cells originating from pupal ovaries of the moth, Antheraea eucalypti, have also been established as a cell line12. This article reports the first successful establishment of a cell line derived from adult tissue of the cabbage looper, Trichoplusia ni.