Effect of aging andP falciparumon the protein and lipid content of the different erythrocyte populations. Control (NRBCs) and uninfected RBCs (URBCs) were density separated by Percoll/sorbitol gradient and ghosts from the various fractions were obtained by lysis and extensive washing with 5 mM NaHPO₄ buffer, pH 8.0; ghosts from infected RBCs (IRBCs) were obtained by lysis with 0.07% saponin (wt/vol). Lipids were extracted, and PLs were quantified by phosphorus determination and cholesterol by thin layer chromatography and densitometric analysis as de-scribed in “Material and methods.” Protein content is expressed as microgram per 10⁷ cells, PL and Cho as micromole per 10¹⁰ cells. Data shown are the mean ± SD of 5 experiments (paired t test for comparison of IRBCs versus very young NRBCs, and young URBCs versus young NRBCs). ^*P < .01.