A reversed phase HPLC method for determination of isorhnchophylline (IRHY) in rabbit plasma was developed. A Shimadzu LC-10A liquid chromatograph equipped with a Shimadzu SPD-10A multiwavelength detector and a Chromatopac LC-10A data processor were used. The analytical column was a 4.6 mm x 150 mm CLC-ODS. The mobile phase was a mixture of methanol-water (95:5), the flow rate was 1 ml.min-1. Detection was performed at UV 254 nm. The calibration curve was linear in the range from 0.016 to 16 micrograms.ml-1 with gamma = 0.9990. The lowest detection limit was 0.016 microgram.ml-1. The precision and accuracy of within-day and day-to-day ranged from 3.8% to 6.9%. The recoveries were 80.5% to 85.1%. The drug concentrtion-time curves of IRHY in rabbits after i.v. of 2 mg.kg-1 and 5 mg.kg-1 were shown to fit a two-compartment open model with half-times of 1.32 +/- 0.6 h and 1.25 +/- 0.09 h respectively. The absorption was fast after intraduodenal administration of IRHY (2 mg.kg-1 and 5 mg.kg-1) to rabbits with half-times of 1.75 +/- 0.18 h and 1.26 +/- 0.20 h, respectively. The bioavailability of IRHY was about 42.4% to 69.4%. The results showed that the method was simple and fast. The absorption and elimination were fast atfer intraduodenal administration or i.v. of IRHY to rabbits.