A novel cytotoxic carbohydrate-conjugated ergosterol (astasin) was found in cells of the colorless euglenoid, Astasia longa. Astasin accounted for about 2.4% of the total lipid of the cells. FAB-MS spectra of astasin showed MH+, 583.3387 (M+, C35H50O7). Astasin was composed of ergosterol (1 eq.),