The Echinostoma caproni-mice system is extensively used as an experimental model for the study of the factors involved in the establishment of chronic intestinal helminth infections. Although several parameters of the immunobiology of the host-parasite system have been studied in detail, the current knowledge of the cellular responses in these infections is still scarce. In the present paper, we analyze the kinetics of the circulating CD3(+) and CD19(+) cell populations and the different T-cell phenotype profiles in mice experimentally infected with E. caproni. Whereas the CD3(+) populations remained stable during the complete experiment, a marked increase in CD19(+) cells was observed from 4 weeks post-infection and beyond. Similarly, a marked increase in CD8(+) cell populations was observed in the 2 week post-infection. Our results show that E. caproni infection in mice alters the peripheral lymphoid cell populations, which may be important to determine the course of the infection. In this sense, CD8(+) cells can be essential in relation to their role as a source of IFN-γ.