The aim of this study was to evaluate the IgG activity in serum and milk samples of experimentally infected lactating ewes with the nematode Teladorsagia circumcincta as well as its relationship to the degree of infection. In a previous study 28 pregnant ewes were divided into two homogeneous groups, with high (H) and low (L) level of parasitism, respectively. Blood and milk samples were taken weekly after lambing until the end of the lactation, 126 days post-partum (pp). IgG against T. circumcincta were measured by means of an indirect ELISA. The kinetic of the immunoglubulins in serum samples showed a very low activity at the beginning but gradually increased throughout the lactation; H group showed higher values most of the sampled days than L group. Contrary, IgG in milk samples remained high during the first month pp, then decreased around 38% and by the end of the study rose again. Antibodies in both samples were correlated and especially during the second month of lactation (r=0.3; p<0.001). With the aim to correlate the immune response and the degree of infection we found an inverse relationship (r=-0.2; p<0.05) during the second month of lactation between eggs and IgG in serum. However the correlation with immunoglobulins in milk was positive, mainly, on the last third of lactation (r=0.2; p<0.01). As a conclusion, the individual detection of total IgG antibodies against T. circumcincta in lactating ewes is highly dependent on the stage of lactation. Therefore, these associations should be confirmed under field conditions.