Abstract: The pharmacokinetics of Qinghaosu and two of its active derivatives was studied by means of the RIA method developed in our laberatory. Artesunate was dissolved in a mixture of 5% NaHCO₃ and 0.9% saline and injected intravenously to 2 dogs at a dose of 6 mg/kg. The serum drug concentration-time course was found to fit a one compartment model with an elimination half-life of 0.45 h as shown in figure 1. The other pharmacokinetic parameters calculated was Cl_T=0.2 L/kg·h, Vd=0.15 L/kg.Artemether, another active derivative of Qinghaosu, was dissolved in peanut oil and given intramuscularly to dogs at doses of 10 mg/kg or 30 mg/kg. The drug was found to be easily absorbed. The serum concentration-time curve is depicted in figure 2. Peak concentrations were reached at 4.0 h after injection of 10 mg/kg and at 1.9 h after a dose of 30 mg/kg with peak serum levels of 0.7 and 3.7 μg/ml, respectively. The half-lives of the elimination phases were shown to be 4.0 h at the dose of 10 mg/kg and 6.5 h at the dose of 30 mg/kg. The data of the serum concentration time course of artemether was also treated by the statistical moment method. The MRT was found to be 7.0 h at the lower dose and 9.4 h at the higher dose.Qinghaosu was ground into very fine powder in a mortar and suspended in peanut oil. The suspension was injected intramuscularly to dogs at the dose of 10 mg/kg. Figure 3 shows that the absorption of Qinghaosu was rapid with peak level of 0.2 μg/ml at 2 h after administration. The half-life of the elimination phase was found to be 1.6 h and the MRT calculated by statistical moment method was 3.3 h.No Qinghaosu was detected by the RIA method in the serum of dogs given the drug rectally or orally.