The immune response of the fetus to maternal infection with Ascaris lumbricoides was studied by estimating IgG and IgM antibodies, using ELISA, in 28 paired samples of mother and cord blood. A. lumbricoides adult male, cuticle and unembryonated egg antigen was used. Toxocara canis larva antigen was used as a specificity control. Presence of IgG in the cord blood does not signify fetal response, but the presence of IgM antibodies does. IgM antibodies to Ascaris adult male antigen were present in 27 out of 28 maternal sera and 1 out of 28 cord sera. All maternal sera and only 6 cord sera showed IgM antibodies against Ascaris cuticle and 20 out of 22 maternal sera and 8 out of 22 cord sera tested, showed IgM antibodies to Ascaris unembryonated egg antigen. Sixteen out of 22 maternal sera and none out of 22 cord sera showed IgM antibody against Toxocara canis antigen, ruling out cross reaction and transplacental leak. The results of our study suggest that the Ascaris infection can spread to the fetus and elicit immune response.