The absolute stereostructures of cicutoxin (1) and related toxic polyacetylenicalcohols, isocicutoxin (2), and virols A (3) and C (4), from Cicuta virosa were determined on the basis of spectroscopic analysis. The CD exciton chirality method was successfully applied to 4-methoxybenzoates of diyne-conjugated polyenyl alcohol systems. Fatal doses of these compounds on mice are also reported.