he surface proteins of trophic (vacuolar and ameboid forms) and cyst forms of two axcnic Blastocystis hominis Brumpt, 1912 isolates were studied. The surface proteins of both forms were biotin-labeled and the soluble proteins from unlabeied and biolin-labcled cells were clcctrophoresed in 10% SDS-polyacrylamide gels under reducing conditions. The clcctrophoresed proteins from biolinylated cells were transferred to nitrocellulose membranes and the avidin-peroxidase-labeled complex was used to identify the surface proteins. In trophic forms, 26 of the 38 soluble proteins, with MW ranging between 30 and >200 kDa, were identified as surface proteins. In cyst forms, 15 of Ihe 29 soluble proteins, with MW ranging between 30 and 193 kDa, were considered as located on the surface of cysts. The comparative analysis of surface protein profiles of both forms showed the presence of a common pattern, composed of 13 bands, and the characteristic proteins of trophic (36, 44, 46, 51, 70, 74, 76, 92, 98, 101, 166, 176 and >200 kDa) and cyst forms (42 and 193 kDa).