Laboratory rats (Rattus norvegicus) were infected with Echinostoma paraensei (Trematoda: Echinostomatidae). The rodents received 150 metacercariae each and blood samples were collected weekly until the fifth week of infection. The blood samples were analyzed for determination of haematocrit, total red blood cells with their dimensions, haemoglobin and haematimetric index (mean corpuscular volume, MCV; mean corpuscular haemoglobin, MCH; and mean corpuscular haemoglobin concentration, MCHC) and platelets. Red blood cells, haematocrit and haemoglobin in the first week had significantly lower levels than those of uninfected (control) rats, suggesting the development of normocytic and normocromic anaemia with anisocytic alteration. The number of eosinophils did not increase significantly among the groups. We concluded that E. paraensei produces haematological alterations in R. norvegicus, causing regenerative anaemia. This system can therefore be a useful model to study the direct and indirect effects of gastrointestinal infections.