Interest in antimyocardial ischemic activity of a graminan-type fructosan with an average molecular weight of 5,000 Da from Ophiopogon japonicus (FOJ-5) has necessitated the development of a sensitive and specific method to study its pharmacokinetics. An HPLC method with modified postcolumn fluorescence derivatization to determine FOJ-5 in plasma was developed in this study. The Shodex Sugar KS-802 high-performance gel column was chosen for separating FOJ-5 from its degradation products and endogenous carbohydrates. The postcolumn procedure involved acid hydrolysis of the column eluate at 150 degrees C, which decreased the detection limit for FOJ-5 from 1 microg to 25 ng, followed by fluorometric reaction with guanidine in an alkaline medium at 90 degrees C. The clearance of FOJ-5 from the bodies of rats following intravenous injection displayed a complex type of kinetics involving at least two compartments, and the half-life of the elimination of FOJ-5 from plasma administered at 15 mg/kg (18.1 min) was quicker than that administered at 50mg/kg (28.9 min). This modified approach can also be used for microanalysis of both nonreducing oligosaccharides and other neutral polysaccharides.