Abstract: The invention provides methods and compositions for inhibiting the development of intracellular parasites by treating such cells with an effective concentration of a magainin, PGLa or XPF peptide under conditions whereby the development of the parasite in the cell is inhibited. The targeted parasites have been found to increase in the accessibility of the plasma membrane of said cell to the peptide, and particularly, to effect an increase in the cytopathic, especially lytic, sensitivity of the cell to the peptide. In one application, the invention provides methods for treating blood infected with a Plasmodium species, by contacting the blood with magainin 2 under conditions whereby the development of the Plasmodium in the infected erythrocytes is inhibited and the infected erythrocytes evidence relatively increased cytolytic sensitivity to the magainin.