The tissue distribution and excretion of artesunate in rats were determined using a radioimmunoassay method. Ten min after i.v. administration of the drug, the highest level was found in the intestine. Levels in other tissues were in the following decreasing order: brain, liver, kidney, testicle, muscle, fat, heart, serum, eyeball, spleen, and lung. However, 1 h after administration, the drug levels dropped significantly in all tissues, but not in the same proportions. High levels remained in the brain, fat, intestine and serum. Drug levels in other tissues were very low. Less than 1% of the dose was found in urine and feces collected during the 24 h period after administration.