Human plasma low density lipoprotein uptake by the urogenital pathogen, Trichomonas vaginalis, was examined. Rapid binding and internalization of 125I-labeled low density lipoproteins by live T. vaginalis was observed at 37 degrees C. Data showing parasite degradation of the internalized apoproteins and lipid accumulation following low density lipoprotein uptake was obtained. Acquisition of low density lipoproteins was by a trichomonad surface protein that possessed a molecular weight of greater than 250,000. The receptor is specific for apolipoprotein CIII, a component of high, low, and very low density lipoprotein subfractions. Low density lipoproteins in a semi-defined medium of trypticase, nucleic acid precursors, vitamins, and maltose promoted T. vaginalis growth and multiplication at rates and levels equal to the yeast extract-trypticase-serum complex medium routinely used for culture of trichomonads. HeLa cell membranes as a source of lipids were unable to sustain T. vaginalis organisms. These data demonstrate host lipoprotein internalization by T. vaginalis via a specific uptake mechanism.