We have characterized by molecular cloning and sequencing a Plasmodium chabaudi antigen that is associated with the membrane of the infected erythrocyte throughout the entire intraerythrocytic cycle. The protein (PcEMA1) has a predicted size of 50 kDa and contains a major tandem repeat array of 16 octapeptides that constitutes almost 30% of the protein. At its amino-terminus, PcEMA1 has a string of hydrophobic residues characteristic of a secreted protein, but does not contain a hydrophobic membrane-spanning segment. The antigen appears to reside on the cytoplasmic face of the erythrocytic membrane. PcEMA1 has a predicted pI of 4.4 and is a potential phosphoprotein.