The purpose of this study was to determine whether metabolites of parasite origin are incorporated into the "knob-like" protrusions of membranes of erythrocytes infected with Plasmodium falciparum. Intraerythrocytic parasites were grown in culture and labelled metabolically with ((35)S)-methionine. Fractions enriched in membranes with knobs and fractions poor in knobs were prepared and analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Labelled components were visualized by autoradiography. Fractions enriched in membranes with knobs showed a consistent relative increase in a labelled band with an apparent relative molecular mass around 70-80 thousand. Membrane-enriched fractions were also tested for glycoprotein components using lectin-binding. No differences were observed between wheat germ agglutinin-binding components in membranes from normal and parasitized erythrocytes. On the other hand, membranes from parasitized erythrocytes showed distinct concanavalin A-binding components around 70-80 thousand relative molecular mass range. Further experiments are required to conclude whether the metabolically labelled protein component observed within the same relative molecular mass range is a membrane-associated glycoprotein identical to the concanavalin A-binding component.