The localization of the antigen-antibody reactions on methacrylate embedded sections of an adult male and female of the nematode Dipetalonema vitae by the indirect immunofluorescence test was found to be as follows: female D. vitae: in the egg-shell and circumference of sections of the microfilariae as well as amorphous structures in the vesica seminalis and vas deferens. In both sexes: partially in the somatic muscle cells according to their glycogen content, the interstitial spaces between the muscle cells and the connecting pseudocoelomic cavity. Reference to the possible application of this technique in the immunofluorescence diagnosis of filariasis is made.