This invention relates to the ribonucleotide reductase of Plasmodium falciparum (Pf RR), to the subunits of Pf RR (Pf R1 and Pf R2), and to compounds comprising peptides derived from the Pf R2 C-terminus sequence that inhibit the action of protozoal RR. The invention provides a method for the prevention and treatment of malaria caused by P. falciparum by controlling the proliferation of P. falciparum comprising administering to a patient at least one peptide according to the invention. Antimalarial compositions are provided which comprise a pharmaceutically acceptable carrier and at least one peptide according to the invention which inhibits the P. falciparum ribonucleotide reductase reduction of ribonucleotides to 2'-deoxyribonucleotides. Also provided are methods for diagnosing malaria and for screening potential antimalarial agents.