Specific serum antibody levels in Leishmania infantum-infected dogs treated with a combination of glucantime and allopurinol were estimated by indirect immunofluorescence and Western blotting. The sensitivity of Western blot was greater than that obtained with immunofluorescence titration. In general, both diagnostic methods concurred with the post-treatment clinical status of the animals. Clinical improvement of successfully treated dogs was related to lower immunofluorescence titers and simpler and/or less reactive immunodetection patterns in Western blotting. The recognition, by infected dogs, of certain low molecular weight antigens, particularly one of approximately 26 kDa, was restricted to pretreatment samples and a single animal in relapse thus apparently constituting an active infection marker.