Hexokinase (EC 2.7.1.1) activity in cell-free Plasmodium berghei was 35 and 5 times higher as compared to normal and P. berghei-infected mouse erythrocytes, respectively. Maximal enzyme activity was present in the cytosolic fraction of the isolated parasite. Manifold purification of parasite hexokinase was achieved with Sephadex G-200. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) revealed parasite enzyme subunit in the molecular weight range of 47 kDa with ATP (adenosine triphosphate) Km of 2 mM. Two out of three mice immunised with the hexokinase fraction were protected upon challenge with live parasites.