There has been controversy whether the plasma protein, alpha1-acid glycoprotein (AGP), is able to inhibit invasion of erythrocytes by P. falciparum merozoites. Because AGP resembles a typical cell membrane sialoglycoprotein, it has been proposed that it can inhibit the parasite from interacting with its sialoglycoprotein receptor on the erythrocyte surface. We therefore isolated and tested samples of AGP obtained from a series of separate individuals. For comparative purposes, we also tested AGP prepared from the plasma of patients with elevated levels of AGP, as well as AGP obtained from two commercial sources. The authenticity and purity of the AGP samples was established by SDS-PAGE, radial immunodiffusion, and crossed immunoelectrophoresis. Our results indicated that none of the nine samples tested had any significant inhibitory effects in our P. falciparum invasion assay system.