GP900 is a unique mucin-like surface glycoprotein of Cryptosporidium parvum merozoites and sporozoites which is a mediator of the cell invasion process and therefore is a potential target for chemotherapeutic competitive inhibitor therapy and vaccine development. The available partial nucleotide sequences of GP900 were compared with the full sequence established for the Iowa isolate of C. parvum to determine whether there was significant sequence variability of GP900 between different isolates of C. parvum. The results showed that GP900 was largely conserved in the 4 isolates studied.