When studies on the biochemistry, molecular biology, and genet- ics of the blood forms of malaria parasites are planned, two features of their biology should be remembered. These forms consist of parasites in a continuous cycle of development, from merozoites through ring-stages, and trophozoites to schizonts. Many species of Plasmodium undergo synchronous development in their natural hosts, but when P falciparum is grown in vitro culture this synchrony is quite rapidly lost. Thus, for work on subjects such as the stage-specific expression of parasite genes, a method for inducing synchrony in cultures of this parasite is a necessary first step. The second feature is that isolates of malaria parasites taken from the wild are likely to contain mixtures of genetically diverse forms (1 , 2 ). It is important, therefore, to estab- lish clones from such isolates to obtain genetically pure lines.