The antigenic properties of somatic (SoP) and excretory–secretory products (ESP) of Echinostoma caproni were studied in experimentally infected rats. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis demonstrated a total of 15 and 9 major polypeptides, in the molecular weight range 10–165 kDa, in SoP and ESP products, respectively. Further analysis revealed some common as well as several unique polypeptides for each type of extract. A total of 2 polypeptides, weighing 58 and 115 kDa, were found in both types of antigen. Indirect enzyme-linked immunosorbent assay analysis using both types of antigens showed that rats developed a weak and slow response in infections with E. caproni. However, the response seems to be mainly directed against excretory–secretory antigens. We have also defined by Western blot 11 and 7 major antigenic polypeptides in SoP and ESP, respectively, that were recognized by sera from experimentally infected rats. Only 2 of these polypeptides were common to both types of antigens. A total of 9 antigenic polypeptides, ranging from 24 to 137 kDa, were found to be characteristic of SoP, whereas 5 polypeptides, weighing from 28 to 117 kDa, were characteristic of ESP. The kinetics of antibody production against discrete polypeptides composing both types of antigens were determined during the course of the infection.