Sporozoite surface protein 2 (SSP2) is a 140-kDa, protective sporozoite surface protein from Plasmodium yoelii distinct from the circumsporozoite protein (CSP). A genomic clone containing the SSP2 gene was isolated and sequenced to determine its size, structural organization and deduced primary amino acid sequence. The coding sequence consists of a single, long open reading frame encoding 826 amino acids. The overall structure of SSP2 is similar to that of the CSP, consisting of a central region of immunogenic amino acid repeats flanked by non-repetitive sequence. SSP2 has one copy of a thrombospondin repeat motif in common with several cell adhesion molecules as well as with the CSP and the thrombospondin related anonymous protein (TRAP) of P. falciparum. Additionally, SSP2 shares substantial sequence similarity to TRAP, suggesting that TRAP is the analogue of SSP2 in P. falciparum.