In this article Chris Newbold and Kevin Marsh describe the evidence for the co-existence of both modified host proteins and of parasite determinants at the infected erythrocyte surface. The stable characteristics of infected cells may in part stem from parasite-induced changes in band 3 molecules, thus explaining some of the cytoadherence properties of uninfected, but abnormal cells (as in sickle-cell disease and diabetes). However, Newbold and Marsh suggest that it is difficult to explain the astonishing diversity of antigens that have been observed at the surface of infected red cells unless such molecules have been synthesized by the parasite.