Microbiology. In the article “A set of independent selectable markers for transfection of the human malaria parasite Plasmodium falciparum” by Choukri Ben Mamoun, Ilya Y. Gluzman, Sophie Goyard, Stephen M. Beverley, and Daniel E. Goldberg, which appeared in number 15, July 20, 1999, of Proc. Natl. Acad. Sci. USA (96, 8716–8720), the authors request the following corrections. In Experimental Procedures (page 8717), under “P. falciparum Transfection and Selection of Transfectants,” there was a typographical error in the concentrations of G418 used for selection. The correct concentrations are 300, 500, or 1,000 μg/ml. Under “BSD Enzyme Assay,” there was a typographical error in the volume of cultured parasitized red blood cells used. The correct volume is 12 ml. In Results (page 8718, line 24 in column 2), the sentence should read: “Varying amounts of either gene were slotted onto the blot, corresponding to the amount of DNA that would be present per microgram of total DNA if there were 1–35 copies of the construct per cell.”