Abstract: An ultraviolet spectrophotometric method with polyamide TLC for the isolation and detection of Aristolochic acid from biological specimens in rats was developed. The method was found to be sensitive and specific and was used for the quantitative determination of Aristolochic acid levels in plasma and tissues.The blood level of Aristolochic acid after intravenous administration in rats was found to decrease in two phases, the distribution and elimination phases, with halflives (α) and (β) of 4 and 34 min, respectively. According to the 2-compartment open model, the pharmacokinetic parameters calculated were as follows: a 0.17 min^-1, β0.02 min^-1, K₁₂ 0.07 min^-1, K₂₁ 0.05 min^-1, V₁ 64 ml/kg, V₂ 84 ml/kg, Vd_(area) 202 ml/kg, Cl_r 4 ml/min/kg. These results show that Aristolochie acid is distributed and eliminated rather rapidly without marked accumulation and the distribution is not wide in the body.Highest drug levels were found in the kidneys and spleen, morderate in heart, brain and liver, and lowest in the lungs and skeletal muscle after intravenous administration in rats, indicating that the drug can pass the blood-brain barrier. After oral administration Aristolochic acid was not detected in plasma with ultraviolet spectrophotometric method, implying that the bioavailability was very low.