Bioassay-guided (cancer cell line) separation of an extract prepared from Narcissus cv. Ice Follies (from The Netherlands) led to the isolation of a new Amaryllidaceae isocarbostiryl, 3-epipancratistatin (1b), as well as narciclasine (2). This Narcissus cultivar was found to be a good source of narciclasine. The structure of 1b was established by high-resolution mass and high-field 2D NMR spectroscopic analyses. Against a panel of murine and human cancer cell lines, 3-epipancratistatin (1b) led to cell growth inhibition (GI50 2.2-0.69 μg/mL) some 100×less than that found for pancratistatin (1a) and narciclasine (2), thereby revealing an important configurational requirement in 1a for strong cancer cell growth inhibition. © 2012 The American Chemical Society and American Society of Pharmacognosy.