Plasmodium vivax-infected blood samples were collected from patients in the field during malaria transmission season. Total RNA of the parasites was extracted by guanidine HCl/cesium chloride centrifugation. mRNA was purified through oligo-dT cellulose. Double stranded cDNA were synthesized with AMV reverse transcriptase by Huynh's method. lambda gt11 phage was used as the vector. A cDNA library of the erythrocytic stage P. vivax was constructed after recombination of DNA and package in vitro.