gp90 levels on the surface of T. cruzi metacyclic trypomastigotes are selectively reduced by the antisense oligonucleotide PS2. Parasites, untreated or treated with PS2, a phosphorothioate oligonucleotide complementary to a sequence of the gp90 coding strand, were incubated with (A) unrelated MAb 1C3, directed to Leishmania gp63, (B) anti-gp90 MAb 1G7, (C) anti-gp82 MAb 3F6, or (D) anti-gp35/50 MAb 10D8. After paraformaldehyde fixation and reaction with fluorescein-labeled anti-mouse IgG, the parasites were analyzed by flow cytometry.