Tetraethylthiuram disulfide (disulfiram) (TETD) and sodium diethylamine-N-carbodithioate (DECD) were examined for their in vitro trypanocidal activity against Trypanosoma cruzi. Benznidazole (BNZ), the drug used clinically for the chemotherapy of Chagas' disease, was used as a positive control. Inhibition assays included evaluation against the epimastigote, trypomastigote, and amastigote forms. Tetraethylthiuram disulfide and its reductive metabolite DECD inhibited 64.6% and 69.7%, respectively, of epimastigotes at a concentration of 50 micrograms/ml after 72 hr and BNZ caused 69.1% inhibition at the same concentration. Both TETD and DECD were not as effective against tissue culture trypomastigotes as BNZ (TETD = 47.7%,; DECD = 46.1%; BNZ = 88.7%) at 50 micrograms/ml after 24 hr. However, TETD and DECD treatment of amastigote-infected 3T3 fibroblasts yielded 60 and 67% inhibition, respectively, as compared to BNZ with an inhibition of 62%. A possible mechanism of action of TETD and DECD is via interference with the essential metal metabolism of T. cruci. Since toxicity data for both TETD and DECD are available and both drugs are active against the parasite, these drugs are candidates for further study to determine if they are of potential clinical interest as a prophylactic or therapeutic agent against Chagas' disease.