The effects of serum and human lipoproteins (HDL, VLDL, LDL) were investigated on the intraerythrocytic cycle of P. falciparum using in vitro synchronized cultures. The reinvasion process of erythrocytes by merozoites and the development until the young trophozoite stage are independent of serum components. In the absence of serum, schizogony did not occur. However, addition of serum before the 24th hour of culture in basal medium restores a normal schizogony. Serum replacement by the different lipoprotein fractions showed that only the HDL fraction was able to assure a complete schizogony as well as a normal erythrocyte reinvasion. No division was observed with the apolipoproteins.