Guan-fu base A, a new antiarrhythmic alkaloid with a structure of C20-diterpenoid, was first isolated from the tuber of Aconitum coreanum (Levl.) Raipaics in China in 1966. An analytical method of GC-ECD has been established in this paper for the determination of its concentration in rabbit plasma in order to study its pharmacokinetics in preclinical pharmacology. Guan-fu base A and the internal standard alprenolol (ALP) was found to react rapidly and quantitatively with trifluoroacetic anhydride (TFAA) to produce derivatives GFA-TFAA and ALP-TFAA which were identified by GC-MSD. An optimal GC-ECD system for the separation and determination of the derivatives following the sample preparation was established. There was a wide linear range of the method from 10-2 x 10(4) ng/ml (r = 0.9984). The average recovery of Guan-fu base A from the spiked plasma was 97.52%. The coefficient of variation of between-day and within-day were less than 9% and 7%, respectively. The method was used to determine Guan-fu base A in the plasma of 15 rabbits following intravenous administration of 3 dosages of 0.4, 2 and 10 mg per kg of body weight.