A new type of antitumor polyacetylenic alcohol, panaxytriol, was isolated from the roots of Panax ginseng C. A. Meyer. A highly sensitive enzyme-linked immunosorbent assay (ELISA) for the determination of panaxytriol was developed, which is capable of measuring as low as 25.6 pg/ml. Anti-panaxytriol antibody was obtained by immunizing rabbits with panaxytriol conjugated with bovine serum albumin using the N-succinimidyl ester method. An enzyme marker was similarly prepared by coupling panaxytriol with horseradish peroxidase. The specificity of this ELISA seems to be primarily toward both the glycol moiety and the diacetylene moiety of the panaxytriol, showing a slight cross-reaction with the other panaxytriol analogues which are structurally different only in C-9,10 positions, but no cross-reaction with the 1,2-decanediol or 3-nonyn-1-ol. The values for panaxytriol concentration detected by this assay were comparable with those detected by the gas chromatography method. The ELISA was about 5000 times more sensitive in detecting panaxytriol. Using this assay, panaxytriol levels were easily determined in the blood of rats. The ELISA may be a valuable tool for studies of the biological and pharmacological properties of the polyacetylenic alcohol, panaxytriol.