The surfaces of the infected erythrocyte (IE) and the merozoite, two 
developmental stages of malaria parasites, expose antigenic determinants to the 
host immune system. We report on surface-associated interspersed genes (surf 
genes), which encode a novel polymorphic protein family, SURFINs, present on 
both IEs and merozoites. A SURFIN expressed in 3D7 parasites, SURFIN4.2, was 
identified by mass spectrometric analysis of peptides cleaved off the surface of 
live IEs with trypsin. SURFINs are encoded by a family of 10 surf genes, 
including three predicted pseudogenes, located within or close to the 
subtelomeres of five of the chromosomes. SURFINs show structural and sequence 
similarities with exported surface-exposed proteins (PvSTP1, PkSICAvar, PvVIR, 
Pf332, and PfEMP1) of several Plasmodium species. SURFIN4.2 of a parasite other 
than 3D7 (FCR3S1.2) showed polymorphisms in the extracellular domain, suggesting 
sequence variability between genotypes. SURFIN4.2 not only was found 
cotransported with PfEMP1 and RIFIN to the IE surface, but also accumulated in 
the parasitophorous vacuole. In released merozoites, SURFIN4.2 was present in an 
amorphous cap at the parasite apex, where it may be involved in the invasion of 
erythrocytes. By exposing shared polymorphic antigens on IEs and merozoites, the 
parasite may coordinate the antigenic composition of these attachment surfaces 
during growth in the bloodstream.