By using an antiserum against isolated cyst walls from resting cysts of the ciliate Colpoda inflata, cyst wall polypeptides have been identified by immunoblotting test. Likewise, an immunoelectron microscopical study on both complete resting cysts and isolated cyst walls to localize the cyst wall proteins recognized by the antiserum, has been carried out. The immunoblotting test showed that three main polypeptide bands were recognized by the antiserum, with tentative molecular weights of 61, 66 and 70 kDa respectively. This methodology provides a better identification of cyst wall proteins after electrophoretic separation of cyst wall samples from ciliate resting cysts.